Peripheral Nervous System (PNS)

What is the peripheral nervous system (PNS)?

any part of nervous system that comes from CNS (brain & spinal cord). Includes all the nerves in the body that lie outside of the spinal cord and brain

What 2 parts make up the PNS?

Somatic Nervous System (SNS)

Autonomic Nervous System (ANS)

What is the role of the somatic nervous system?

Controls voluntary or conscious activity

What is the role of the Autonomic nervous system?

Controls involuntary or unconscious activity e.g. breathing

What makes up the Autonomic NS?

Cardiac muscle

Smooth muscle

Glands

Define nerves

Cord-like structures consisting of bundles of axons (& associated neuroglia) OUTSIDE of CNS

Define epineurium

The outermost layer of dense irregular connective tissue surrounding a peripheral nerve. It usually surrounds multiple nerve fascicles as well as blood vessels which supply the nerve. Epineurium is continuous with dura mater of CNS.

What are nerves surrounded by?

Connective tissue (epineurium being the outmost layer) & blood vessels.

Define fascicles

Bundles of axons (makes up neurons)

Define tract

A bundle of neurons inside the CNS.

How are nerves classified?

Based on their origin - either 1 of 2:

Cranial Nerve or

Spinal nerve

Define neuron

a specialized cell transmitting nerve impulses; a nerve cell.

List the 3 types of neurons that can be present in a nerve

Sensory nerve

Motor nerve

Mixed nerve - sensory & motor (all spinal nerves)

How many cranial nerves are there?

12 numbered pairs

Define cranial nerve

nerves inside the cranial cavity, directly connected to the brain (bypass spine)

Where are cranial nerves located?

Visible on the front of the brain (ventral surface)

3 types of cranial nerves

Sensory

Motor

Mixed

Type & function of olfactory nerve

Sensory nerve, carries impulses from odour receptors (smell)

Type & function of optic nerve

Sensory. Carries impulses from rods & cones in the retina of eye.

List the 3 cranial nerves that control eye movement

oculomotor

Trochlear

Abducens

Type & function of oculomotor (3) nerve

Motor. Eyeball movement, upper eyelid, pupil size & shape

Type & function of trochlear (4) nerve

Motor. Eyeball movement.

Type & function of Abducens (6).

Motor. Eyeball movement

Type & function of Trigeminal nerve

Mixed. Three branches.

Sensory impulses from scalp, face, mouth & teeth.

Somatic motor impulses to muscles of chewing.

list 3 types of Trigeminal nerve branches

Ophthalmic nerve

Maxillary nerve

Mandibular nerve

Type & function of Facial nerve.

Mixed.

Sensory - taste from tongue.

Somatic motor - to muscles of facial expressions & neck

Autonomic motor - lacrimal glands (tears) & salivary glands.

Type & function of vestibulocochlear nerve?

Sensory. Sense of hearing & equilibrium.

2 branches of vestibulocochlear nerve?

Vestibular - equilibrium

Cochlear - hearing

Type & function of glossopharyngeal (throat) nerve

Mixed.

Sensory - taste, (touch, pain temp = ear). Baroreceptors & chemoreceptors.

Somatic motor - contracting pharynx for swallowing

Autonomic motor - saliva secretion

Function of baroreceptors

Receptor sensitive to pressure changes. Blood pressure.

Chemoreceptors

Detect blood gas levels & changes, chemicals in the

Type & function of vagus nerve

Mixed.

Sensory - tase, (touch, pain, temp =ear), proprioceptors, baroreceptors, chemoreceptors, hunger, fullness & discomfort (abdominal organs), speaking & swallowing (Larynx & pharynx).

Autonomic - lungs, heart, glands of respiratory, gi tract, smooth muscle.

Proprioceptors

signal information to the central nervous system about position and movement of body part. Located in muscles, tendons, joints & inner ear

Type & function of accessory nerve

Motor. Movement of head, neck & shoulder muscles

Type & function of hypoglossal nerve

Motor - impulses to tongue for speech, food manipulation & swallowing.

How many pairs of spinal nerves are there?

31. with 5 groups

Name the spinal nerve groups

Cervical nerves - C1-C8 (8 total)

Thoracic nerves - T1-T12 (12 total)

Lumbar nerves - L1-L5 (5)

Sacral - S1-S5 (5)

Coccygeal Co1 (1)

Type & function of spinal nerves.

Spinal nerves are all mixed. They connect the CNS to sensory receptors, muscles & glands.

Where are spinal nerves leave the spine?

Most pass out through the vertebral foramen (holes on side of spine) & then branch.

There are also a group of roots that hand from spinal cord from the 2nd lumbar vertebra in the spinal cord.

Spinal Nerve roots

Each spinal nerve is "rooted" to the spinal cord at the front & back (made up of bundles of neurons). The part that enters or leaves spinal cord = root

Posterior spinal nerve root vs anterior

Posterior = back, has sensory axons. Cell bodies contained within root ganglion.

Anterior = front, has motor axons. Cell bodies contained within grey matter of spinal cord.

Root ganglion

enlarged section of posterior spinal nerve root that contains cell bodies of sensory neurons

Explain the disease affecting spinal nerve roots

Shingles. Virus attacks neurons within posterior & anterior root. Virus can remain dormant in posterior root ganglia. Vaccine available.

Spinal Plexuses

an intermingling of fiber fascicles from adjacent spinal nerves to form a network. Reconnect to other nerves. Nerves emerging from a plexus contain axons from several different spinal nerves.

Where are spinal plexus present?

Several regions, excluding T2-T12

Sacral plexus

a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg and foot, and part of the pelvis. Extends from base of spinal nerves (L4,L5 & S-S5) down through pelvis to leg.

Sciatic nerve

Part of the sacral plexus. Nerves of the skin & muscles of posterior & lateral thigh, leg & foot.

Which part of body is responsible for reflexes?

The grey matter of brain stem & spinal cord.

What are the 2 types of reflexes?

Somatic & Autonomic (visceral)

Somatic reflexes

Contraction of skeletal muscles e.g. stretch & flexor reflexes

Autonomic (visceral) reflexes

Contraction of smooth or cardiac muscle or stimulation of glands. Not generally consciously perceived.

Why are reflexes (e.g. patellar reflex) tested clinically?

Gives us info on the health of nervous system.

Reflex arc

the nerve pathway involved in a reflex action, including at its simplest a sensory nerve and a motor nerve with a synapse between

Process of a reflex arc

1. Sensory receptor detects stimulus

2. Sensory neuron prorogates to CNS

3. Regions of grey matter in CNS act as integrating centre

4. Motor neuron prorogaties from CNS to receptor

5. Effector responds to action potential & performs characteristic

Monosynaptic reflex arc

synapse directly with a motor neurone

Polysynaptic reflex arc

synapse with one or more interneurons & a motor neuron

Interneuron

a neuron which transmits impulses between other neurons,, especially as part of a reflex arc.

Autonomic nervous system purpose

Integrates info & controls regulatory processes to maintain homeostasis.

Interoreceptors

Sensory receptors that detect internal environment e.g. baroreceptor

Autonomic Nervous System (ANS) process

ANS gives input to CNS from interoreceptors (e.g. baroreceptors). Motor neurons activate cardiac or smooth muscle to contract or relax or activate glands to increase/decrease secretions to bring homeostasis. (e.g. baroreceptors give input to CNS that BP is high & blood vessels dilate to reduce.

2 divisions of the Autonomic Nervous System

Sympathetic

Parasympathetic

Which part of the brain integrates the Autonomic nervous system

Hypothalamus

Sympathetic NS

regulates excitatory processes. part of the nervous system that serves to accelerate the heart rate, constrict blood vessels, and raise blood pressure. (Fight or flight)

Parasympathetic NS

regulates inhibitory processes. Part of the involuntary nervous system that serves to slow the heart rate, increase intestinal and glandular activity, and relax the sphincter muscles. (Rest & relaxation)

Autonomic NS Features

2 motor neurons (somatic = 1)

Many organs have dual access from both branches (sympathetic & parasympathetic) e.g. heart, eyes

Some organs receive only sympathetic e.g. blood vessels, sweat glands

Thermoreceptors

Detect changes in temperature.

Nociceptors

Respond to stimuli from physical or chemical damage to tissue

Osmoreceptors

Detect osmotic pressure of body fluids

Define effector

Any part of the body that produces a response (from the nervous system)

What type of reflex is the patellar reflex?

Stretch reflex

Which cranial nerves control the eyeball?

3, 4 & 6

Longest & thickest nerve in the body innervating most of the lower limb

Sciatic nerve

Cranial reflex

reflexes utilizing the muscles of the head, or cranial nerves

Spinal reflex

The withdrawal reflex (nociceptive or flexor withdrawal reflex) is a spinal reflex intended to protect the body from damaging stimuli

What type of reflex is the "hot stove" reflex?

A spinal reflex