detects environmental changes that impact the body, then works together with the endocrine system to respond. It is responsible for all our behaviors, memories, and movement.
the excitable characteristic of nervous tissue
It is able to accomplish for all our behaviors, memories, and movement which allows for the generation of nerve impulses (action potentials)
3 fundamental steps in the nervous system
Receive, process and transmit information by manipulating the flow of charge across their membranes.
the “functional unit” of the nervous system, they form complex processing networks within the brain and spinal cord.
- do not generate or conduct nerve impulses.
- (glial cells) play a major role in support and maintain nutrition of the brain, but they do not manipulate information. They maintain the internal environment
•Forming the Blood Brain Barrier (BBB)
•Forming the myelin sheath (nerve insulation) around neuronal axons
•Making the CSF that circulates around the brain and spinal cord
•Participating in phagocytosis
4 types of neuroglia in the CNS:
4) Ependymal cells
- form and circulate CSF
- support neurons in the CNS
•Maintain the chemical environment (Ca2+ & K+)
- participate in phagocytosis
- produce myelin in CNS
2 types of neuroglia in the PNS:
1) Satellite cells
2) Schwann cells
- support neurons in PNS
- produce myelin in PNS
the process of forming a myelin sheath which insulates and increases nerve impulse speed.
It is formed by Oligodendrocytes in the CNS and by Schwann cells in the PNS.
refers to the loss or destruction of myelin sheaths around axons. It may result from disease, or from medical treatments such as radiation therapy and chemotherapy.
When an axon is injured, the neurolemma aids regeneration by forming a ________ ______ that guides and stimulates regrowth of the axon.
The outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath (sheath of Schwann).
The cell bodies of neurons can only be repaired through _____ after an injury.
Nodes of Ranvier
- are the gaps in the myelin sheath.
Each Schwann cell wraps one axon segment between two nodes of Ranvier.
Divisions of the Nervous System
Includes; the central nervous system (CNS) and The peripheral nervous system (PNS)
Central Nervous System (CNS)
- consists of the brain and spinal cord.
- Most signals that stimulate muscles to contract and glands to secrete
Peripheral Nervous System (PNS)
- consists of all nervous tissue outside the CNS, including nerves, ganglia, enteric plexuses, and sensory receptors.
- divided into:
1) A somatic nervous system (SNS)
2) An autonomic nervous system (ANS)
3) An enteric nervous system (ENS)
Somatic Nervous System (SNS)
- Somatic sensory
- Somatic motor
(afferent) neurons that convey information from sensory receptors.
Sensory or afferent neurons
convey APs into the CNS through cranial or spinal nerves. Most are unipolar.
Motor or efferent neurons
convey APs away from the CNS to effectors (muscles and glands) in the periphery through cranial or spinal nerves. Most are multipolar.
Interneurons or association neurons
mainly located within the CNS between sensory and motor neurons. They integrate (process) incoming sensory information from sensory neurons and then elicit a motor response by activating the appropriate motor neurons. Most interneurons are multipolar in structure.
(efferent) neurons that conduct impulses away from the CNS towards the skeletal muscles.
Autonomic Nervous System (ANS)
1. Sensory neurons that convey information from autonomic sensory receptors located primarily in visceral organs.
2. Motor neurons under involuntary control conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands.
•the sympathetic division
•the parasympathetic division
Enteric Nervous System (ENS)
the “brain of the gut”, involuntarily controls GI propulsion, and acid and hormonal secretions.
are small masses of neuronal cell bodies located outside the brain and spinal cord, usually closely associated with cranial and spinal nerves.
Parts of the neuron
1) A cell body
2) An axon
4) Axon terminals
- (little trees) are the receiving end of the neuron.
- short, highly branched structures that conduct impulses toward the cell body.
- They also contain organelles.
- nucleus surrounded by cytoplasm.
- neurons contain organelles such as lysosomes, mitochondria, Golgi complexes, and rough
ER for protein production (in neurons, RER is called Nissl bodies) .
- conduct impulses away from the cell body toward another neuron or effector cell.
- Contains Axon hillock, initial segment, and trigger zone.
The axon and its collaterals end by dividing into many fine processes
Synaptic end bulbs
The tips of some axon terminals swell into
The site of communication between two neurons or
between a neuron and another effector cell
the gap between the pre and post-synaptic cells.
Synaptic end bulbs on the axon terminals of presynaptic neurons contain many tiny membrane-enclosed sacs that store packets of neurotransmitter chemicals.
Electrical impulses or action potentials (AP)
cannot propagate across a synaptic cleft. Instead, neurotransmitters are used to communicate at the synapse, and re-establish the AP in the postsynaptic cell.
Slow axonal transport
supplies new axoplasm (the cytoplasm in axons)
Fast axonal transport
occurs in an anterograde (forward) and a retrograde (backward)
direction moves organelles and synaptic vesicles from the cell body to the axon terminals.
direction moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled.
have several dendrites and only one axon and are located throughout the brain and spinal cord. The vast majority of the neurons in the human body.
have one main dendrite and one axon.They are used to convey the special senses of sight, smell, hearing and balance. As such, they are found in the retina of the eye, the inner ear, and the olfactory area of the brain.
Unipolar (pseudounipolar) neurons
contain one process which extends from the body and divides into a central branch that functions as an axon and as a dendritic root and often employed for sensory neurons.
based on the number of processes (axons or dendrites) extending from the cell body.
based on electrophysiological properties (excitatory or inhibitory) and the direction in which the AP runs.
_____ _______of the brain and spinal cord is formed from aggregations of myelinated axons from many neurons. The lipid part of myelin imparts the white appearance.
(gray because it lacks myelin) of the brain and spinal cord is formed from neuronal cell bodies and dendrites.