Introduction to the Nervous System

what are the divisions of the nervous system (cells → tissues → organs → systems)?

neurons/glia → nerves → spinal cord & brain

what are afferent (sensory) neurons?

transmit impulses from receptors in the skin, sense organs, muscles, joints, and viscera toward the CNS

what are efferent (motor) neurons?

transmit impulses from CNS to effector organs (muscle, glands)

what are interneurons (association neurons)?

not specifically motor or sensory

communication links

~90% of all neurons

what are the structural divisions of the nervous system?

central nervous system (brain & spinal cord)

peripheral nervous system (nerves & ganglia)

where does the spinal cord run in an adult?

from inferior to brainstem to superior border of 2nd lumbar vertebra in adults

what is the cervical enlargement of the spinal cord?

brachial plexus

nervous supply to upper extremity

what is the lumbar enlargement of the spinal cord?

lumbar plexus

nervous supply to lower extremity

what is the conus medullaris?

conical portion between 1st and 2nd vertebrae

what is the cauda equina?

dorsal and ventral rootlets - “horse’s tail”

what is the filum terminale?

extension of pia mater that anchors spinal cord to coccyx

what is contained in the gray matter of the spinal cord?

soma, axons, and dendrites of interneurons, sensory and motor neurons (neurons collecting info from the body)

what is contained in the white matter of the spinal cord?

myelinated axons of motor and sensory neurons

what are the cranial nerves?

peripheral nerves that arise from the brain

what are the spinal nerves?

anterior (ventral) root + posterior (dorsal) root

together = mixed spinal nerve (anterior primary rami, posterior primary rami)

cranial nerve I

olfactory → sensory - smell

cranial nerve II

optic → sensory - vision

cranial nerve III

oculomotor → mixed - eye movement/proprioception

cranial nerve IV

trochlear → mixed - eye movement/proprioception

cranial nerve V

trigeminal → mixed - chewing/sensation (teeth, skin)

cranial nerve VI

abducens → mixed - eye movement/proprioception

cranial nerve VII

facial → mixed - facial movements/taste

cranial nerve VIII

vestibulocochlear → sensory - hearing/equilibrium

cranial nerve IX

glossopharyngeal → mixed - saliva secretion/taste

cranial nerve X

vagus → mixed - respiration movements and sensation

cranial nerve XI

accessory → mixed - head movement/proprioception

cranial nerve XII

hypoglossal → mixed - tongue movement/proprioception

what are the characteristics of the spinal nerves?

connect CNS to PNS

31 pairs - 8 C, 12 T, 5 L, 5 S, 1-2 C

pass through intervertebral foramen

named for the level where they exit the spinal cord

what is the setup of a basic spinal reflex loop?

receptor → sensory neuron → integration center → motor neuron → effector

what is a dermatome?

the region of the skin that one spinal segment supplies

what is a myotome?

a group of muscles innervated by roots from one spinal segment

what are the peripheral cutaneous nerves?

nerves that terminate after finishing their motor innervations, travel from deep under muscle to superficial to innervate the skin

what are the functional divisions of the nervous system?

somatic nervous system (SNS) (skeletal muscle, skin)

autonomic nervous system (ANS) (smooth muscle, cardiac muscle, glands)

what are the divisions of the autonomic nervous system?

sympathetic (thoracolumbar)

parasympathetic (craniosacral)

what are the responses of the autonomic nervous system?

changes in pupil size

accommodation for near vision

dilation of blood vessels

adjust rate and force of heart beat

movements of the GI tract

secretion of most glands