Nervous System Flashcards
What are the two main divisions of the nervous system and what do each include?
1) Central nervous system - includes all nervous tissue associated with the brain and spinal cord
2) Peripheral nervous system - includes all neural tissue outside the CNS
What is the CNS responsible for?
integrating, processing, coordinating sensory input and motor output. Also higher functions like intelligence, memory, learning, and emotion.
What are the two main divisions of the PNS (think about the direction of the flow of information)?
Afferent: somatic sensory, visceral sensory, and special sensory fibres carry information about some aspect of the environment to the CNS
Efferent: somatic and autonomic fibres carry motor information to elicit some response.
What are the two main divisions of the efferent division of the PNS and what are they responsible for?
1) Somatic nervous system: controls skeletal muscle contraction
2) Autonomic nervous system: controls activities of internal organs (via smooth muscle, cardiac muscle, or glands)
What are the two cell types of the nervous system and what are the main difference between them?
1) Neuron
2) Neuroglia
Main difference is that the neurons are excitable while the neuroglia are not. Glia also retain the ability to undergo cell division while neurons do not.
What is the difference between gray matter and white matter?
Gray matter is neural tissue made of the cell bodies of neurons while white matter is neural tissue made of myelinated axons
What are the types of neuroglia in the CNS and what are their roles?
1) Oligodendrocytes: myelinate CNS axons and provide structural framework
2) Astrocytes: maintain BBB, provide structural support, regulate ion, nutrient, and dissolved gas concentrations, absorb and recycle NTs, and form scar tissue after injury
3) Microglia: remove cell debris, waste, and pathogens by phagocytosis
4) Ependymal cells: line ventricles and central canal, assist in producing, circulating, and monitoring CSF
What are the types of neuroglia in the PNS and what are their roles?
1) Satellite cells: surround neuron cell bodies in ganglia and regulate dissolved gas, nutrient, and NT levels in ganglia
2) Schwann cells: surround and myelinate all axons in the PNS, and participate in repair process after injury
What are the clusters of cell bodies in the PNS called?
Ganglia
What are the four structural classifications of neurons?
1) anaxonic - no anatomical clues to differentiate axons and dendrites. Found in the CNS and special sense organs
2) bipolar - dendrites fuse to form one long dendrite and the cell body lies between the dendrite and a single long axon. Found in special sense organs for relaying sight, smell, and hearing.
3) pseudounipolar - continuous dendritic and axonal processes with the cell body lying off to the side. Found in sensory neurons of the PNS.
4) multipolar - several dendrites and a single axon. Most common in the CNS (eg. motor neurons)
What are the functional classifications of neurons?
1) Sensory - collect information concerning the external or internal environment
2) Motor - stimulate or modify the activity of a peripheral tissue, organ, or organ system
3) interneuron - analysis of sensory input and coordination of motor output
What is a neuronal pool?
A group of interconnected neurons with specific functions
What is a neural circuit?
The specific pattern of connectivity found within a neuronal pool.
What are the two major types of synapses found in the nervous system?
1) Chemical/vesicular synapse
2) Electrical/non-vesicular synapse
List the sequence of events that occur at a chemical synapse:
1) Action potential arrives at presynaptic membrane
2) Neurotransmitter is released from axon vesicles
3) NT diffuses across synapse
4) NT binds to postsynaptic membrane
5) Binding causes a change in permeability of the post synaptic membrane to one or more ion species
6) Change in permeability results in an action potential at the next neuron
List the sequence of events at an electrical synapse:
1) presynaptic membrane of one neuron is tightly bound to the postsynaptic membrane of the next neuron
2) this binding permits the passage of ions from one neuron to the next
What is another name for Schwann cells?
Neurolemmocytes
What is the primary purpose of myelin?
Increase the conduction speed of an action potential or neural impulse.
What type of nervous tissue are most brain cancers derived from and why?
Most brain tumours arise due to cell division and neuroglia are the only nervous tissue capable of undergoing cell division and regeneration.
What is a reflex? What is a reflex arc?
- an immediate, involuntary motor response
- the progression from sensory receptor to peripheral effector
What are the two main ways we classify reflexes?
1) monosynaptic: involves a single segment of the spinal cord, minimal delay between stimulus and response, and presents the same every time
2) polysynaptic: involves integration of input from several spinal segments, longer delays between stimulus and response.
Describe what takes place in the stretch reflex:
a monosynaptic reflex arc:
- proprioceptors in muscle spindles send afferent information to the dorsal root of the spinal cord
- afferent fibre conducts through posterior gray horn
- afferent fibre synapses with efferent motor neuron at anterior gray horn
- motor neuron projects to muscle fibres to stimulate a contraction of the appropriate muscle
Describe what takes place in the withdrawal reflex:
a polysynaptic reflex arc:
- nociceptors or thermoreceptors are activated by a stimulus
- sensory neuron sends information to the spinal cord where it synapses with an interneuron
- this interneuron can be excitatory or inhibitory; if it is inhibitory, it usually projects to another interneuron to inhibit it which disinhibits the motor neuron. If it is excitatory, it projects to another interneuron to excite it to excite/stimulate the motor neuron on one side and inhibit the antagonists
- the excited motor neuron stimulates the muscle fibres to contract on the side of the response
- the inhibited motor neuron generally projects to an antagonist - no activation of the antagonist
When do anterior horns increase in size?
When the number of muscles innervated by a spinal segment increases
What is the difference between a tract and a column of white matter?
Tract: bundles of CNS axons that share a common origin and destination
Column: several tracts that form an anatomically distinct mass in the spinal cord
What is the shallow longitudinal groove along the dorsal surface of the spinal cord called? What is the deep crease along the ventral surface called?
- posterior median sulcus
- anterior median fissure
What are the two major enlargements of the spinal cord?
The cervical enlargement and the lumbosacral enlargement. These areas have a larger amount of gray matter than other areas of the spinal cord due to the presence of interneurons.
What is the name of the slender, fibrous tissue that extends from the end of the spinal cord to the coccyx?
- filum terminale
What is the function of the filum terminale?
- provide longitudinal support to the spinal cord as a component of the coccygeal ligament
What is the cauda equina?
Composed of the filum terminale and the long dorsal and ventrak riits that extend caudally
What are the main roles of the spinal meninges?
1) provide protection
2) physical stability
3) shock absorption
The spinal meninges and the cranial meninges are continuous at what location on the skull?
At the foramen magnum
What tissue type makes up the three layers of the spinal meninges?
Dura: dense, irregular connective tissue covered by simple squamous epithelium
Arachnoid: simple squamous epithelium
Pia: elastic and collagen fibres
What structure of the spinal cord contains axons crossing from one side to the other?
Gray commissures
How are spinal nerves named?
Cervical: for the vertebra directly following them
Thoracic and Lumbar: for the vertebra immediately preceding them