Human Anatomy - Nervous System
The function of the nervous system is to control and integrate all body activities within limits that maintain life
What are the three basic functions?
– Sensing changes with sensory receptors (sensory input)
– Interpreting and remembering those changes (integration)
– Reacting to those changes with effectors (motor output)
The events in Sensory-Motor Integration
- Stimulus is received by sensory receptor.
- Impulse travels through sensory neurons to Central Nervous System (CNS).
- CNS interprets information and determines motor response.
- Motor impulse travels out from CNS through motor neurons.
- Motor impulse reaches muscle fibers and response occurs.
What are the Functional classifications of Neurons?
Sensory Neurons (afferent neurons)
- form afferent division of the Peripheral nervous system (PNS)
- deliver information from sensory receptors to the CNS
- most are unipolar with the cell bodies located in the sensory ganglia outside the CNS
Motor Neurons (efferent neurons)
- carries instructions from the CNS to the peripheral effectors
- Most are multipolar with the cell bodies located in the CNS
- situated between sensory and motor neuron and mostly confined to the CNS
Remember the acronym S.A.M.E
Stands for >
S = Sensory neurons (are)
A = Afferent neurons
M = Motor neurons (are)
E = Efferent neurons
A typical synapse comprises of?
- Presynaptic cell – transmits the message
- Postsynaptic cell – receives the message
Commonly involve the release of a neurotransmitter
What are Neuroglia (glial cells)?
Neuroglia are cells of the Central Nervous System (CNS) and Peripheral Nervous System (PNS) that support and protect the neurons.
What are the neuroglia of the central nervous system.
- Astrocytes – maintain the blood brain barrier; provide support; regulates ion, nutrient and neurotransmitter concentrations; assists with injury repair
- Oligodendrocytes – myelinates CNS axons (wrap around the axons)
- Microglia – remove waste, pathogens and debris (clean up crew)
- Ependymal cells – line brain ventricles and canal of spinal cavity; regulates cerebrospinal fluid (line the cavities)
What are the neuroglia of the peripheral nervous system.
- Satellite cells – surround neuron cell bodies in ganglia
- Schwann cells – cover all axons in the PNS; assist with injury repair
What are the four principal parts of the brain?
- Diencephalon (thalamus & hypothalamus)
- Brain-stem (medulla, pons & mid-brain)
The Cerebrospinal fluid....
- Surrounds and bathes exposed surfaces of the CNS
- Acts to cushion delicate structures, support the brain, and transport nutrients, chemical messengers and waste products
- 97% off the brains weight is reduced
- around 150 ml of CSF.
The cerebrum of the brain is?
(state some functions & facts)
- Largest region of the brain (~80% mass)
- Consists of a right and left hemisphere connected by the corpus callosum
- Responsible for higher mental functioning
- The area of neural cortex covering the cerebral hemispheres is referred to as the cerebral cortex
What are the landmarks on the Cerebrum?
Fissure - An elongate groove or opening
Sulcus - A groove or furrow
Gyrus - A prominent fold or ridge of neural cortex
- Longitudinal fissure
- Central sulcus
- Lateral sulcus
- Precentral gyrus (folds)
- Postcentral gyrus (folds)
There are two layers of the Cerebrum, they are?
Gray Matter of the Cerebrum
- Found in the cerebral cortex and in the deeper cerebral nuclei
- Consists of nerve cell bodies, unmyelinated axons and dendrites
- Characterized by numerous folds and grooves.
White Matter of the Cerebrum
- Lies beneath the neural cortex and around the cerebral nuclei
- Consists of dendrites and myelinated axon.
There are five (5) lobes of the Cerebrum Cortex, they are?
Frontal - voluntary control of skeletal muscle, concentration, planning
Parietal - cutaneous and muscular sensation, understanding speech, emotions, interpretation of textures and shapes
Temporal - interpretation of auditory sensations, storage (memory) of auditory and visual experiences
Occipital - eye coordination, perception of vision
Insula - memory, integrates cerebral activities
What are the primary areas of the Cerebral Cortex?
- Motor areas
- Sensory areas
- Association areas
The cerebral cortex has these areas that send out motor signals, areas that receive sensory signals and areas which associate both (motor & sensory) signals together and store them.
The thalamus and the hypothalamus are located where?
The Diencephalon in the brain
The thalamus is responsible for...
The final relay for sensory information projected to the primary sensory cortex. It relays information between the cerebral nuclei and the cerebral cortex
In simple terms - information travels up the spinal cord which goes via the thalamus then sent to primary sensory cortex.
The hypothalamus is responsible for....
- controling muscle contraction,
- nervous and endocrine function,
- emotions, hormonal control and behavioural drives,
- body temperature regulation
- coordination between voluntary and autonomic functions
The cerebellum is the automatic processing center of the brain that has two main functions, which are?
- Adjustment of postural muscle control
- Programming and fine movements controlled both consciously and subconsciously
The Cerebellums main features are?
- Left and right hemispheres
- Anterior and posterior lobes
- Cerebellar nucleus
- Arbor vitae (tree of life)
What is one of the 9 different peptide hormones the pituitary glands releases? And how many are from the anterior & posterior division?
Anterior Division - releases 7
- Adrenocorticotropic (ACTH)
- Thyroid Stimulating hormone (TSH)
- Follicle Stimulating hormone (FSH)
- Lutenizing hormone (LH)
- Growth hormone (GH)
Posterior Division - releases 2
- Oxytocin (OT)
- Antidiuretic hormone (ADH)
The Pons (bridge) links the cerebellar hemispheres with the other parts of the brain and spinal cord, what does it contain?
- Sensory and motor nuclei for four cranial nerves
- Nuclei controlling respiration
- Tracts interconnecting other portions of the CNS
The medulla oblongata is continuous with the spinal cord and connects the brain and spinal cord, what does it contain?
- Nuclei with autonomic control of visceral activities
- Sensory and motor neuclei of 4 cranial nerves
- Relay station along sensory and motor pathways
What are the sensory functions?
- Sensory specific receptors provide information to the CNS about inside and outside conditions
Sensory function can be divided into two areas:
- General senses
- Special senses
What is Transduction? Can be divided into three steps.
Transduction is the translation of a stimulus into an action potential (a change in temperature to an electrical signal which will then travel alone an axon).
- Alteration of receptor potential by arriving stimulus
- Sensitization of the sensory neuron
- Transmission of an action potential to the CNS via an afferent fibre
The sensory functions can be divided into two areas; Special and General senses. What are the senses in each area?
- Gustation (taste)
General Senses Can be:
- Exteroceptors – information about external environment
- Proprioceptors – position of skeletal muscles and joints
- Interoceptors – monitor visceral organs and functions
Receptors are divided into the subcategories
- Nociceptors - pain
- Thermoreceptors - temperature
- Mechanoreceptors - stretching, compression and distortion
- Chemoreceptors - chemical receptors
- olfaction - smell (located in nasal cavity)
- gustation - taste (superior surface of tongue, & portions of the pharynx & larynx)
What is the accessory structure of the eye?
- Eyelid (palpebrae) - closes to protect the eye
- Eyelashes - very sensitive area
- Medial and lateral canthus
- Lacrimal gland - produces fluid
- Lacrimal gland ducts
- Lacrimal sac
Anatomy of the eye
- Orbital fat
- Anterior cavity
- Posterior cavity
- Fibrous tunic – Sclera
- Vascular tunic – Choroid
- Neural tunic – Retina
- Ciliary body
- Optic disc
The chambers of the eye
- Anterior cavity in front of lens, has an anterior and posterior chamber and contains a substance called aqueous humour (transparent).
- Posterior cavity behind lens and contains vitreous humour (aka vitreous chamber)
- Canal of Schlemm (schleral venous sinus)
What does the lacrimal apparatus produce?
it produces the fluid/tears which washes medially across the eye, and drains away and down the back of the nose.
What is the pathway of a nerve signal in the retina?
- Light travels through retina & absorbed through to the back
- Rods & cones transduce (convert) light into action potentials
- Rods & cones excite bipolar cells
- Bipolars excite ganglion cells
- Axons of ganglion cells form optic nerve leaving the eyeball (blind spot)
- then to thalamus & then the primary visual cortex
What is the anatomy of the ear?
Divided into the external, middle ear and inner ear
External structures include:
- external auditory canal,
- tympanic membrane
The Middle ear, also referred to as the tympanic cavity is filled with air and mucous lined, it also contains the auditory ossicles that connect the tympanic membrane to the receptors of the inner ear. What are the three bones in the middle ear?
Where is the Semicircular canals and the cochlea located?
The inner ear
What is the hearing process?
- Sound waves vibrate tympanic membrane
- Tympanic membrane vibrates auditory ossicles
- Oval window movement produces pressure waves in vestibular ducts
- Pressure waves distort basilar membrane
- Distortion of basilar membrane vibrates hair cells against tectorial membrane
- Hair vibration stimulates cochlear branch of vestibulocochlear nerve
Simple terms: vibrations travel in from the outer ear to the middle ear, through to the inner ear. The vibrations are then picked up/distorted bouncing signals on the cochlear branch.
The inner ear - Equilibrium
- Provided by receptors of the vestibular complex
- Semicircular ducts provide information about rotation of the head via the ampulla
- Capable of detecting direction and speed of movement
- Movements cause distortion and therefore stimulation of the cupula within the ampulla