Chapter 13: The Peripheral Nervous System

sensory receptors

specialized cells that convert a stimulus into an electrical signal that the nervous system can process and interpret

general senses

• detected by receptors distributed throughout the body

• e.g. touch, temperature, and pain

special senses

• detected by specialized organs like the eyes, ears, nose, and tongue

• e.g. vision, hearing, smell, taste, and balance

Tonic Receptors

generate a prolonged response, maintaining a sustained firing rate as long as the stimulus is present

Phasic Receptors

respond rapidly to the onset of a stimulus but quickly decrease their firing rate, even if the stimulus persists

adaptation

decrease in receptor sensitivity over time when exposed to a constant stimulus

Cortical‑terminating pathways

• sensory information about touch, pain, temperature

• special senses

Non‑cortical terminations

• end in brainstem or spinal cord

• autonomic functions, reflex arcs, emotional responses

olfactory nerve

• nerve I

• Carries sensory information for the sense of smell

optic nerve

• nerve II

• Carries visual information from the retina to the brain

oculomotor nerve

• nerve III

• Controls most eye movements

trochlear nerve

• nerve IV

• Controls superior oblique muscle movement, movingt the eye down and out

trigeminal nerve

• nerve V

• Mixed nerve for both sensation (face, mouth, teeth) and motor function (muscles of mastication)

abducens nerve

• nerve VI

• Controls lateral rectus muscle movement (moves the eye outward)

facial nerve

• nerve VII

• Controls facial expression, taste sensation, salivary and lacrimal glands

vestibulocochlear nerve

• nerve VIII

• Controls hearing and balance

glossopharyngeal nerve

• nerve IX

• Controls swallowing, taste from the posterior tongue, and provides sensory input from the middle ear

vagus nerve

• nerve X

• Controls swallowing, speech, heart rate, digestion, and other parasympathetic functions

hypoglossal nerve

• nerve XI

• controls tongue movement; allows for speech articulation, swallowing, and food manipulation during chewing

accessory nerve

• nerve XII

• rotates the head, flexes the neck; shoulder movement, including shrugging

cervical plexus

• Spinal Nerves: C1-C4

• Phrenic nerve, lesser occipital nerve, great auricular nerve

brachial plexus

• Spinal Nerves: C5-T1

• Axillary nerve, ulnar nerve, Radial nerve

lumbar plexus

• Spinal Nerves: T12-L4

• Femoral nerve, Obturator nerve

sacral plexus

• Spinal Nerves: L4-S3

• Sciatic nerve, Pudendal nerve

receptor

component that detects a stimulus

sensory neuron

• aka the afferent neuron

• carries the signal from the receptor to the central nervous system

integration center

• acts as a processing center

• typically located in the central nervous system, often the spinal cord

motor neuron

• aka the efferent neuron

• carries the signal from the integration center to the effector

effector

the muscle or gland that carries out the response

Somatic Reflexes

• Result in muscle contraction and movement.

• Examples: Withdrawal reflex (removing a hand from a hot surface), knee-jerk reflex.

Autonomic (Visceral) Reflexes

• regulate involuntary internal processes.

• Involve smooth muscles, cardiac muscles, and glands as effectors.

• Examples: Pupillary light reflex, regulation of blood pressure, digestion

cranial reflex

• Involve cranial nerves and have their integration center within the brain or brainstem.

• Examples: Pupillary light reflex, salivation, gag reflex

spinal reflex

• Involve spinal nerves and have their integration center within the spinal cord.

• Examples: Stretch reflex, withdrawal reflex

stretch reflex

Resists muscle lengthening (e.g., prevents limb from collapsing under weight)

withdrawal reflex

Protects body from harmful stimuli by quickly withdrawing the affected limb

reciprocal innervation

• when one muscle contracts (agonist), its opposing muscle (antagonist) simultaneously relaxes

• prevents opposing forces from working against each other