The Peripheral Nervous The Peripheral Nervous System System

Peripheral Nervous SystemPeripheral Nervous System

31 pairs of spinal 31 pairs of spinal nerves nerves

12 pairs of cranial 12 pairs of cranial nervesnerves

All of the smaller All of the smaller nerves that branch nerves that branch from larger nervesfrom larger nerves

Afferent and Efferent PathwaysAfferent and Efferent Pathways

Afferent Pathways

Efferent Pathways

Spinal NervesSpinal Nerves

31 Pairs31 Pairs

Numbered according to the level of the vertebral Numbered according to the level of the vertebral column at which they emerge from the spinal column at which they emerge from the spinal cavity cavity

Lumbar, Sacral, and Coccygeal nerves descend Lumbar, Sacral, and Coccygeal nerves descend from their point of origin at the lower end of the from their point of origin at the lower end of the spinal cordspinal cord

Lower end of the cord is called the Lower end of the cord is called the cauda cauda equina, equina, which means “horses tail” in Latinwhich means “horses tail” in Latin

Structure of Spinal NervesStructure of Spinal Nerves

Mixed Nerves (contain Mixed Nerves (contain motor and sensory fibers)motor and sensory fibers)

Attach by means of two Attach by means of two short rootsshort roots

Dorsal rootDorsal root Has ganglion (cell bodies)Has ganglion (cell bodies) Carries sensory neruons Carries sensory neruons

Ventral rootVentral root Carries motor neuronsCarries motor neurons

Dorsal and Ventral RamiDorsal and Ventral Rami

Soon after each spinal nerve emerges from the Soon after each spinal nerve emerges from the spinal cavity, it forms several large branches, spinal cavity, it forms several large branches, each of which is called a ramus. each of which is called a ramus.

Dorsal Ramus Dorsal Ramus Supplies somatic motor and sensory fibers to serveral Supplies somatic motor and sensory fibers to serveral

smaller nervessmaller nerves

Ventral Ramus Ventral Ramus More complexMore complex

Rami of Spinal NervesRami of Spinal Nerves

Nerve PlexusesNerve Plexuses

Ventral rami of most spinal nerves Ventral rami of most spinal nerves subdivide to form complex networks called subdivide to form complex networks called plexuses.plexuses. Cervical plexus Cervical plexus Brachial plexus Brachial plexus Lumbar plexus Lumbar plexus Sacral plexusSacral plexus

Damage to one Damage to one spinal nerve does spinal nerve does not mean complete not mean complete loss of function in loss of function in any one region. any one region.

Dermatomes and Myotomes Dermatomes and Myotomes

Each skin surface Each skin surface area supplied by area supplied by sensory fibers of a sensory fibers of a given spinal nerve is given spinal nerve is called a dermatome.called a dermatome.

A myotome is skeletal A myotome is skeletal muscle or group of muscle or group of muscles that receives muscles that receives motor axons from a motor axons from a given spinal nerve.given spinal nerve.

Dermatome Distribution of Spinal Dermatome Distribution of Spinal NervesNerves

Myotomes and Body MovementMyotomes and Body Movement

Cranial Nerves Cranial Nerves 12 pairs 12 pairs

Connect to the undersurface of the brain Connect to the undersurface of the brain

Pass through small foramina (holes) in the cranial cavity Pass through small foramina (holes) in the cranial cavity and skulland skull

Identified by names and numbers Identified by names and numbers

3 Types3 Types Mixed Mixed Sensory Sensory Motor Motor

Divisions of the Divisions of the Peripheral Nervous Peripheral Nervous

System System

Somatic Motor Nervous System Somatic Motor Nervous System

All the voluntary motor pathways outside All the voluntary motor pathways outside the CNS (pathways to skeletal muscles)the CNS (pathways to skeletal muscles)

Single motor neuron whose axon stretches Single motor neuron whose axon stretches from the cell body in the CNS all the way from the cell body in the CNS all the way to the effectorto the effector

Stimulates effectors by means of the Stimulates effectors by means of the neurotransmitter acetylcholineneurotransmitter acetylcholine

Somatic Reflexes Somatic Reflexes

The action that results from a nerve impulse passing The action that results from a nerve impulse passing over a reflex arc is called a reflex.over a reflex arc is called a reflex.

Predictable response to a stimulus Predictable response to a stimulus

May or may not be consciousMay or may not be conscious

Somatic reflexes are contraction of skeletal muscleSomatic reflexes are contraction of skeletal muscle

Autonomic reflexes consist of contractions of smooth or Autonomic reflexes consist of contractions of smooth or cardiac muscle, or secretion by glandscardiac muscle, or secretion by glands

Used in the diagnosis of diseaseUsed in the diagnosis of disease

Knee Jerk ReflexKnee Jerk Reflex

Autonomic Nervous SystemAutonomic Nervous System

Regulates involuntary effectorsRegulates involuntary effectors

Major function of the ANS is to regulate Major function of the ANS is to regulate heartbeat, smooth muscle contraction, and heartbeat, smooth muscle contraction, and glandular secretion in ways to maintain glandular secretion in ways to maintain homeostasis. homeostasis.

Sympathetic and Parasympathetic Sympathetic and Parasympathetic DivisionsDivisions

Sympathetic and Parasympathetic have Sympathetic and Parasympathetic have separate pathwaysseparate pathways

Effectors may have dual innervation, that Effectors may have dual innervation, that is they have input from both types of is they have input from both types of pathwayspathways

Parasympathetic – “rest-and-repair”Parasympathetic – “rest-and-repair”Sympathetic – “fight-or-flight”Sympathetic – “fight-or-flight”

Autonomic Conduction PathsAutonomic Conduction Paths