Human Physiology: Mammalian Physiology Midterm 2 (ch 6-11) Flashcards

• Completely within CNS
• Complex branching that allows for communication with other neurons
• Can be very small
• afferent

•somatic motor and autonomic neurons
 Somatic motor division- controls skeletal muscles
 Autonomic division- controls smooth and cardiac muscles, exocrine glands, some endocrine glands, and some types of adipose tissue
• Enlarged axon terminals

the region where an axon terminal communicates with its postsynaptic target cell
 presynaptic cell- the neuron that delivers a signal to the synapse
 postsynaptic cell- the cell that receives the signal
 synaptic cleft- gap between presynaptic cell and postsynaptic cell that is filled with extracellular matrix whose fibers hold the cells in position

 Graded potential -> action potential -> synapse (axon terminal)

 use chemical signals to find target (growth factor, molecules in the extracellular matrix, membrane proteins along growth cones)
 the axons of embryonic nerve cells send out special tips (growth cones) that extend through the extracellular compartment until they find their target cell
 connection between neurons must be active or the synapse will degrade
 babies are born with the same nerve cells as adults but they develop by making neural connections

 support staff of the nervous system
 10-50x the number of cells as neurons
 Provide physical support
 Provide some communication and important biochemical support to neurons
 PNS: Schwann cells and satellite cells
CNS: astocytes, microglia, oligodendrocytes, ependymal cells

PNS glial cells
o Form myelin sheaths
o Leaves nodes of Ranvier (tiny gaps) between the myelin-insulated areas when wrapping around an axon
 Allows for a tiny section of axon membrane to be in direct contact with the extracellular fluid which plays a role in the transmission of electrical signals along the axon
o Secrete neurotrophic factors

PNS glial cells
o Nonmyelinating Schwann cell
o Support cell bodies in ganglion (clusters of nerve cell bodies outside the CNS)
o Provides structure and physical support

o Highly branched glial cells that form a functional network by communicating with one another through gap junctions
o Several roles that the terminals could have
 Take up and release chemicals
 Provide neurons with substrates for ATP production to help maintain homeostasis in CNS
 Surround blood vessels and become part of the blood-brain barrier

CNS glial cell
modified immune cells that reside permanently in the CNS
o Scavenge whatever they think shouldn't be there
o Can release reactive oxygen species that can damage the CNS
 Plays a role in neural diseases

CNS glial cell
o Key difference between Schwann cells
 Schwann can only wrap around one axon
 Oligodendrocytes can wrap around several axon

CNS glial cell
o Specialized cells that create a selectively permeable epithelial layer that separates the fluid compartments of the CNS
o Source of neural stem cells
o Communicate through chemical signals

a substance composed of multiple concentric layers of phospholipid membrane
 Acts as insulation around axons which speeds up their signal transduction
• Gap junctions connect the myelin membrane layers and allow the flow of nutrients and information from layer to layer

 Depolarization
• Move down concentration gradient
• Membrane potential increases (from lightly negative initial potential from Na+ going to ICF from ECF)
 Hyper polarization
• Remove K+ from ICF or add Cl- to ICF
• need to move very few ions to see a change in membrane potential
 Gated ion channels
• Named after the ion they are trying to move
mechanical, chemical or voltage
threshold voltage and speed for channel to open varies with channel type

variable-strength signals that travel over short distances and lose strength as they travel through the cell
 More stimulus = more signals being opened up= stronger signal
o If strong enough, reaches trigger zone
 If signal reaches threshold, Na+ channels open and AP starts
 If not strong enough nothing will happen

 Excitability- the ability of a neuron to respond to a stimulus and fire an action potential
 Depolarizes membrane (local current flow)
 Brings closer to action potential threshold
 Positive ions (Na+)

 Hyperpolarizes membrane
 pushes away from action potential
 negative ions

a stimulus that is below threshold by the time it reaches the trigger zone
no AP

 The membrane of neuron cell body has open leak channels that allow positive charge to leak out into the extracellular fluid
 Cytoplasm provides resistance to the flow of electricity

a signal that is strong enough to cause and action potential by the time it reaches the trigger zone

o Brief, large depolarization
o Long distances
o Signal strength is constant
o Starts at trigger zone, reaches end of axon
o Occur as a maximal depolarization (if the stimulus reaches threshold) or do not occur at all (if the stimulus is below threshold)
o All about moving ions
rising, peak, and falling phases
o A neuron could fire >1000 times without affection ion gradients

• Overshoots following the concentration gradient because its following the electrical gradient as well
• Permeability to Na+ increases
• Na+ voltage-gated channels open

• Na+ follows gradients to equilibrium point
• Na+ channels close
• K+ channels open

• Permeability to K+ increases
• K+ voltage-gated channels open
• Follows electrical and concentration gradient out of axon
• Undershoots (hyperpolarization) following concentration gradient
• K+ channels close
• Na resets during refractory period
o 1/100,000 K+ leave cell during falling phase of action potential

 Once an AP has started, cannot fire another for 1-2 msec.
 Absolute or relative refractory periods

• Na+ channels are not reset
• AP cannot happen
• AP moving from trigger zone to axon terminal cannot overlap and cannot travel backwards

• Some Na+ channels have reset, K+ channels are still open
• Stronger than normal graded potential could trigger AP

 Diameter of the axon affects speed of AP
• Larger axon diameter = less resistance = faster signal propagation
o Myelination
 Minimize ion leakage by minimizing contact with ECF
• Decreases membrane capacitance

blocked Na+ channels (anesthetics, neurotoxins)
ion concentrations in the ECF, specifically K+
hyperkalemia (too much K+ in ECF, depolarizes cells, lowers AP threshold)
hypokalemia (too little K+ in ECF, hyperpolarizes cells, raises AP threshold)

o Pass signal through gap junctions directly from the cytoplasm of one cell to another
 Through pre and post synaptic cells
o CNS, glial cells, muscle, pancreatic beta cells
o Rapid signaling
o Relatively uncommon compared to chemical signals

o Majority of synapses
neurocrine signals
 May act as neurotransmitters, Neuromodulators, or neurohormones

• Usually act as paracrine signals (Can act as autocrine signals, but not common)
o Target cells located close the neuron that secreted them
• Act at both synaptic & non-synaptic sites (glial cells, etc. , not blood)
• Slower, longer lasting response than neurotransmitters

neurocrine receptor
• Ionotropic receptors
o Receptor-channels mediate rapid responses by altering ion flow across the membrane
• Neurotransmitter binds to channel, opens channel, allows ion to move into postsynaptic cell
• Rapid responses
• Quick to degrade

• Metabotropic receptors
o Regulate the opening and closing of ion channels
• Use second messenger system
• Slower responses than ligand-gated ion channels, longer lasting

 Act at a synapse- does not move through blood
 Quick, short acting response
 Seven classes based on structure
 PNS: Only 3 major neurocrines
 CNS: Release a variety of neurocrines
 Use a variety of receptors with specific names

can be peptide proteins or smaller neurotransmitters
o The action potential depolarizes the axon terminal
o The depolarization opens voltage-gated Ca2+ channels, and Ca2+ enter the cell
o Calcium entry triggers exocytosis of synaptic vesicle contents
o Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell
o Neurotransmitter binding initiates a response in the postsynaptic cells
o endocytosis on the membrane then cell breaks away

divergent or convergent
integration of signals
spatial summation, temporal summation, postsynaptic inhibition, synaptic integration, presynaptic inhibition, presynaptic facilitation

a single presynaptic neuron branches, and its collaterals synapse on multiple target neurons

a group of presynaptic neurons provide input to a smaller number of postsynaptic neurons

type of nerve signal integration
o multiple excitatory neurons fire, their graded potentials separately are all below threshold
o Graded potentials arrive at a trigger zone together and sum to create and a suprathreshold signal
o An action potential is generated

type of nerve signal integration
o 2 subthreshold graded potentials from the same presynaptic neuron can be summed if they arrive at the trigger zone close enough together in time

type of nerve signal integration
o The inhibitory postsynaptic potential (IPSP) counteracts the excitatory postsynaptic potential (EPSP)
o The summed potentials are below threshold, so no action potential is generated

type of nerve signal integration
o When multiple signals reach a neuron, postsynaptic integration creates a signal based on the relative strengths and durations and compares the integrated signals to the threshold

type of nerve signal integration
o Activity in an inhibitory neuron decreases neurotransmitter release
o Allows selective modulation of collaterals and their targets
 One can be inhibited while others are unaffected

type of nerve signal integration
o Input from an excitatory neuron increases neurotransmitter release by the presynaptic cell

 Gray matter
• Unmyelinated nerve cell bodies, dendrites, & axon terminals
• Organized in layers or clusters (nuclei)
 White matter
• Myelinated axons and few cell bodies
• Tracts – bundles of axons that connect different regions of the CNS
 Brain and spinal cord are soft, contains little extracellular matrix
 Bone
• Brain – Skull, Spinal cord – Vertebral column

• 3 layers of membrane
• Connective tissue
• Lie between bones and tissues
• Stabilize neural tissue and protect from bruising by bones
• contains Dura mater, arachnoid, and pia mater

• Dura mater
o Thickest
o Drains blood from brain through cavities (sinuses)
• Arachnoid
o Middle membrane
cerebrospinal fluid is found between pia mater and arachnoid membrane
• Pia mater
o Thin membrane
o Arteries that supply blood found here, interstitial fluid found here

secreted into the ventricles and flows throughout the subarachnoid space (between pia mater and arachnoid membrane), where it cushions the CNS

protection for CNS- buoyancy and padding

chemical- closely regulate the extracellular environment and exchange materials with the interstitial fluid of the CNS

• Separates interstitial fluid and blood
• Barrier is necessary to isolate the body’s main control center from potentially harmful substances in the blood and from blood borne pathogens
• Capillaries with highly selective membranes

• Highway for information between brain & rest of body (skin, joints, and muscles)
• Contains neural networks for locomotion
• Self-regulated pathways for spinal reflexes
• Can also send signals to brain
• Divided into 4 regions: cervical, thoracic, lumbar, and sacral
 White matter- consists of tracts of axons carrying information to and from the brain
 Gray matter- sensory and motor nuclei

 Similar in structure to the spinal cord
 Oldest, most primitive part
 Can be divided into white and gray matter (similar to spinal cord)
 Reticular formation, medulla, pons, midbrain, cerebellum, diencephalon, hypothalamus, cerebrum

diffuse collection of neurons that extend throughout the brain stem
• Sleep/arousal, muscle tone, breathing, pain

• AKA medulla oblongata
• Transition between brain & spinal cord
• White matter- ascending somatosensory tracts bring sensory information to the brain and descending corticospinal tracts convey info from the cerebrum to the spinal cord
o 90% of corticospinal tracts crossover the midline to the opposite side of the body in pyramids section
o Create left and right brain that control the opposite side of the body
• Gray matter- Involuntary responses
o Blood pressure, Breathing, Swallowing, Vomiting

• Relay station between cerebrum & cerebellum
• Works with medulla to help regulate breathing

• Relay station for auditory and visual reflexes
• Controls eye movement

• Second largest part of brain
• Contains more nerve cells than rest of brain combined
• Process sensory info
• Coordinate movement

• Between brain stem and cerebellum
• Contains 2 main sections (thalamus and hypothalamus) and 2 endocrine structures (pituitary and pineal glands)

• Activates sympathetic nervous system (catecholomine (flight or fight) release and maintaining blood glucose concentrations)
• Maintains body temperature
• Controls body osmolarity
• Controls reproductive functions
• Controls food intake
• Influences behavior and emotion with limbic system
• Influences cardiovascular control center in medulla
• Secretes trophic hormones that control the release of hormones in the pituitary gland

• Very furrowed surface (especially compared to mice/rats that have a very smooth surface)
• Two hemispheres connected by corpus callosum (structure formed by axons passing from one side of the brain to the other)
o Ensures the 2 hemispheres communicate and cooperate
• Cerebral gray matter
o Cerebral cortex- outer layer of the cerebrum (contains layered neurons where higher brain function arises)
 Perception
 Movement
o Basal ganglia
 Movement
o Limbic system
• Cerebral white matter- axons themselves
o white and grey matter alternate in layers

• Lots of sensory information comes in and the thalamus will relay the information
o Thalamus can modify and integrate the information
o Relay station
 Eyes, Ears, Spinal cord, Motor (from cerebellum)
 Projects fibers to the cerebrum where the information is processed
 All sensory information from the lower parts of the CNS pass through the thalamus
o Integrating center

surrounds brain stem
 Link between higher cognitive functions (like reasoning) and more primitive emotional responses (fear)
 Emotion (amygdale and cingulated gyrus)
 Memory(amygdale, cingulated gyrus, hippocampus)
 Learning (hippocampus)

• asymmetrical distribution of functional specialization
• each lobe has special functions not shared by the matching lobe on the opposite side
• the specialization can change, you can build new connections
• Right handed = left brain dominant

integrating center for sensory information and a decision-making region for many types of motor output

sensor

 directs skeletal muscle movement
 Part of efferent division of nervous system
 3 types: skeletal movement, neurocrine signals, and visceral responses
• neurocrine and visceral responses are coordinated primarily by the primary motor cortex and the medulla

• skeletal movement- controlled by the somatic motor division
• neurocrine signals- neurohormones secreted into the blood by neurons located primarily in the hypothalamus and adrenal medulla
• visceral responses- the actions of smooth and cardiac muscle or endocrine and exocrine glands (muscles, organs)

part of behavioral state systems

neurons that originate in the reticular formation in the brain stem and project their axons to large areas of the brain

o Named based on neurotransmitter they release
o Influence motivation, memory, sleep, etc.

• Easily reversible state of inactivity characterized by lack of interaction with external environment
• sleep releases molecules that assist your immune system
• non-REM sleep (deep sleep) and REM sleep

o alternating daily pattern of rest & activity
o Regulated by suprachiasmatic nucleus of the hypothalamus
o Feedback loop
 Genes turn on, direct protein synthesis
 Protein accumulates, turns off genes
 Protein degrades, turning back on genes
o Synchronized with the sensory info about light cycles received through the eyes

 Variable and specialized
• Receptors can be stimulated by other stimuli sometimes
 Includes non-neural cells
 Accessory structures
 Convert stimulus into neural signal

• Physical area covered by sensory neuron
• Primary sensory neuron- one receptive field associated with one sensory neuron
• Secondary sensory neuron- synapses in the CNS neuron

• Sensory neuron sends info to thalamus
• Thalamus processes & relays to appropriate CNS structure
 Synapse in the thalamus and then signal is passed on to another location

o Inhibitory modulation
o Suprathreshold stimulus pushed below perceptual threshold

 Sensory modality (nature of sensory stimuli)
 Sensory location
 Stimulus intensity
 Stimulus duration

helps your body tell signals apart
o The modality is indicated by which sensory neurons are activated and by where the pathways of the activated neurons terminate in the brain
 Connected to specific regions of the sensory cortex

helps your body tell signals apart
connected to specific regions of the sensory sortex
lateral inhibition

helps your body tell signals apart
• The number of receptors activated
• Frequency of action potentials coming from those receptors (frequency coding)

helps your body tell signals apart
• Longer stimulation à more APs in sensory neuron

adaption, tonic receptors, phasic receptors

o Primary neuron response is proportional to stimulus strength
o Pathway closest to the stimulus inhibits neighbors
o Inhibition of lateral neurons enhances perception of stimulus
o Secondary neuron that is most activated had post synaptic inhibition which causes only the strongest cells from the sensory neuron

slow adapting receptors that fire rapidly when first activated, then slow and maintain their firing as long as the stimulus is present

rapidly adapting receptors that fire when they first receive a stimulus but cease firing if the strength of the stimulus remains constant

• Pain, temperature, and coarse touch cross the midline of the spinal cord
o Synapse onto their secondary neurons shortly after entering the spinal cord
• Fine touch, vibration, and proprioception pathways cross the midline in the medulla
• Sensory pathways synapse in the thalamus
• Sensations are perceived in the primary somatic sensory cortex

touch, proprioception (awareness of surroundings), temperature, nociception

 Responds to:
• Stretch: Ruffini corpuscle- slow adaption
• Pressure: Merkel receptors- slow adaption
• Stroking: Meissner’s corpuscle- rapid adaption
• Vibration: Pacinian corpuscle- rapidly adapting phasic receptors
o Can respond to a change in touch then ignore it

 Free nerve endings in subcutaneous layer of skin
 More cold than warm receptors
• Cold receptors – sense below body temp
• Warm receptors – sense between body temp & 45°C
• > 45°C – pains receptors activated
 Slowly adapt between 20-40°C, otherwise do not adapt

 Respond to damaging stimuli via pain and itch
• Chemical, mechanical, & thermal
 Found throughout body, not just skin
 2 pathways: Reflexive protective (spinal cord), Conscious sensation in the cerebral cortex (CNS)

• Pain is not a direct stimulus, but a perception
• Nociceptors send info to CNS via A-delta & C fibers
o Fast pain – sharp, localized – rapidly signals CNS via myelinated A-delta fibers
o Slow pain – dull, diffuse – signals CNS via unmyelinated C fibers
• Signals limbic system & hypothalamus too
• Treated with aspirin, opioids or other drugs, electrical stimulation, or severing sensory nerves

o Signal carried to CNS via subtype of C fiber
o Antagonistic interaction with pain
 When something itches, we scratch it creating a sensation of pain to stop the itch
• Works in the other direction too

extension of forebrain that sends info to olfactory cortex
 Receives input from the primary olfactory neurons

o Primary sensory neurons (olfactory sensory neurons) synapse with secondary in olfactory bulb which moves towards the olfactory cortex via the olfactory tract
 can be routed to the hippocampus and amygdale (limbic system involved in emotion and memory)
 bypasses the thalamus

 Odorant receptors- protein receptor that is sensitive to a variety of substances
• G-protein coupled receptors
• Largest gene family in vertebrates

 Each olfactory sensory neuron has one type of odorant receptor
 Convergence of many primary sensory neurons to a few secondary neurons in olfactory bulb which modifies the info and sends it to the olfactory cortex
 Olfactory cortex uses hundreds of signals in different combinations to create perception of smells

 Sweet – nutritious organic molecules
 Umami – glutamate (MSG)
 Bitter – toxic organic molecules
 Sour – excess H+
 Salty – excess Na+

 Taste buds (taste receptors) located in surface of tongue
 Not neural cells, specialized taste cells
 Taste bud= 50-150 taste cells + support and regenerate cells
 Taste pore is the only area of the cell that is exposed to the external environment
 Dissolved particles (food dissolved by saliva) interact with apical membrane protein on a taste cell
 Each taste cell is sensitive to one taste

 4 cell types:
• 1- support cells- may sense salt when Na+ enters through Na+ channels
• 2- receptor cells- respond to sweet, bitter, and umami sensations
o Releases ATP through gap junctions and ATP acts on both sensory neurons and neighboring presynaptic cells
• 3- presynaptic cells- perceive sour, synapse with sensory neurons
• 4 basal cells- give rise to new taste cells

• ligands activate the taste cell
• various intracellular pathways are activated
• Ca2+ signal in the cytoplasm triggers exocytosis or ATP formation
• Neurotransmitter or ATP is released
• Primary sensory neuron fires and action potentials are sent to the brain

o Perception of energy delivered by sound waves
o Sound- the brain’s interpretation of the frequency and duration of sound waves
 Interpretation of frequency (pitch), intensity and amplitude (loudness), and duration

Tympanic membrane= eardrum

smell, taste, hearing, equilibrium, vision

o Energy from sound waved in the air becomes mechanical vibrations, then fluid waves in the cochlea
o The fluid waves open ion channels in hair cells (sensory receptors for hearing)
o Ion flow into hair cells creates electrical signals that release neurotransmitter (chemical signal) which triggers action potentials in the primary auditory nerves

• Conductive
o No sound transmission through external or middle ear
o Perfect suction cup around ear can pop the ear drum
• Central
o Damage to neural pathways or cortex- caused by strokes, brain trauma
• Sensorineural
o Damage to inner ear structures
o 90% of hearing loss

 Balance- Position of body in space
 Stimuli- Changes in gravity and acceleration
 3 Semicircular canals

• Rotational acceleration
• Horizontal- shaking head side to side (“no”)
• Superior- nodding back and forth (“yes”)
• Posterior- head towards right or left shoulder

• Vestibular hair cells release neurotransmitters to the primary sensory neurons of the vestibular nerve which lead to the cerebellum for equilibrium processing

o Translation of light reflected from objects into a mental image
 Light enters eye, lens focuses light on retina
 Photoreceptors transform light into electrical signal
 CNS processes electrical signals into visual images

size of pupil (radial muscles control the contracting and expanding with changes)

change shape of lens (accommodation, ciliary muscles flatten and curl lens)

• Light from a fixation point passes through the lens which focuses the light on the retina and fovea
• The projected image is upside down on the retina
o Visual processing in the brain reverses the image
• Retina photoreceptors are organized in layers
• Light strikes the photoreceptors in the fovea directly because overlying neurons are pushed aside
• There are 3 types of cone pigment (blue, green, and red), each with a characteristic light absorption spectrum

• Two types of bipolar cells
o Bipolar cells- begins signal processing when glutamate is released from photoreceptors
 Light-on (excited by glutamate inhibition)
 Light-off (excited by glutamate release)
• Ganglion cells- Receive signals from area of photoreceptors on retina called visual field
• Visual fields are smaller towards fovea, larger towards outer portions of retina

 Sensory system- monitors the internal and external environments and initiates reflex responses
 Cognitive system- resides in the cerebral cortex and is able to initiate voluntary responses
 Behavioral state system- resides in the brain and governs sleep-wake cycles and other intrinsic behaviors

conversion of stimulus energy into information that can be processed by the nervous system
o Often the opening or closing of ion channels

 Controls skeletal muscle
 “Voluntary” division of nervous system

consists of axon terminals, motor end plates on the muscle membrane, and Schwann cell sheaths
• 3 components
o The motor neuron’s presynaptic axon terminal filled with synaptic vesicles and mitochondria
o Synaptic cleft
o Postsynaptic membrane of the skeletal muscle fiber

 Controls smooth muscle, cardiac muscle, many glands, some adipose tissue
 “Involuntary” division of nervous system
sympathetic or parasymptathetic

autonomic pathways
• Dominant in stressful situations
• Fight or flight response
• Provides stimulation or control during most of the time

autonomic pathways
• Dominant in calm situations
• Rest & digest response
• Active almost all the time

• homeostasis-
o Works closely with the endocrine and behavioral state system to maintain homeostasis in the body
 Homeostatic control centers: hypothalamus (contains osmoreceptors and thermoreceptors), medulla, pons
• Reflex responses- some autonomic reflexes are capable of taking place without input from the brain (spinal reflexes)
• Behavioral responses- emotional influences on autonomic functions

• one autonomic branch is excitatory and the other branch is inhibitory
• Often sympathetic & parasympathetic control act in opposite directions on same tissue
• Regulate by altering amount of control given to each branch
• Receptor type can determine response

Synapse between a postganglionic autonomic neuron & target cell
varicosities
o No high concentration of receptors in target cells during autonomic response (like in other responses)

swollen area at distal end of postganglionic axons
 Filled with neurotransmitters and mitochondria
 Will surround the target tissue

o Neuroendocrine tissue associated with sympathetic nervous system
o Secretes epinephrine- system wide response
 Secretes norepinephrine, catecholamines, and epinephrine during development
o Neural and endocrine tissue (similar to pituitary gland)