Peripheral n.s.

Peripheral Nervous Peripheral Nervous SystemSystem

Peripheral Nervous Peripheral Nervous SystemSystem

The peripheral nervous system is made up of all the nerves (sensory & motor) that are found outside of the central nervous system

The cell bodies of these neurons are found in the brain, spinal cord, and in nerve ganglia (enlarged portions of a nerve)

Sensory nerves are made up of long dendrites of sensory neurons

Motor nerves are made up of the long axons of motor nerves

Mixed nerves are made up of both motor and sensory neurons and relay messages back and forth to the CNS

Nerves of the PNS can also be classified as cranial or spinal nerves

Human Nervous SystemHuman Nervous System

Cranial NervesCranial Nerves

There are 12 pairs of cranial There are 12 pairs of cranial nerves nerves

Nerves I and II are nerves of Nerves I and II are nerves of the cerebrum, and III through the cerebrum, and III through XII are nerves of the brainstem XII are nerves of the brainstem

Leaving the underside of the Leaving the underside of the brain, they pass through small brain, they pass through small holes in the skull holes in the skull

Functions Of Nervous Functions Of Nervous SystemSystem

Olfactory Olfactory

ooSensory nerve involved in smell (olfaction) Sensory nerve involved in smell (olfaction)

Optic Optic

ooSensory nerve involved in vision Sensory nerve involved in vision

Focusing and pupil constriction Focusing and pupil constriction Oculomotor Oculomotor

ooMotor nerve which controls movements of Motor nerve which controls movements of the eyeball (ciliary muscles), elevation of the eyeball (ciliary muscles), elevation of upper eyelid, focusing, and pupil upper eyelid, focusing, and pupil constriction constriction

Trochlear Trochlear

oo Motor nerve which controls Motor nerve which controls the movement of the eye (down & out) the movement of the eye (down & out) via the superior oblique muscle via the superior oblique muscle

Trigeminal Trigeminal

oo Mixed nerve, being the chief Mixed nerve, being the chief facial sensory nerve and the motor facial sensory nerve and the motor nerve of the chewing muscles nerve of the chewing muscles

oo Has three main branches, the Has three main branches, the opthalmic, maxillary, and mandibular opthalmic, maxillary, and mandibular nervesnerves

Abducens Abducens

ooextra-oculomotor nerve which innervates the extra-oculomotor nerve which innervates the lateral rectus muscle to abduct (turn out) the eye lateral rectus muscle to abduct (turn out) the eye

Facial Facial

ooMixed nerve which controls the muscles of facial Mixed nerve which controls the muscles of facial expression, taste, tongue, and salivary glands expression, taste, tongue, and salivary glands

Acoustic / Vestibulocochlear Acoustic / Vestibulocochlear

ooBranches into two sensory nerves, the cochlear Branches into two sensory nerves, the cochlear and vestibular relating to hearing and balance and vestibular relating to hearing and balance respectively respectively

Neuromuscular controlNeuromuscular control

Neuromuscular Control: Neuromuscular Control:

Control of striated (voluntary) Control of striated (voluntary) muscles is essential to maintain muscles is essential to maintain homeostasis homeostasis

The network of motor nerves which The network of motor nerves which (somatic pathways) innervate the (somatic pathways) innervate the individual muscles by releasing individual muscles by releasing acetylcholine at the motor end acetylcholine at the motor end plates of the neuromuscular junction plates of the neuromuscular junction

Autonomic Pathways & Autonomic Pathways & Neurovisceral controlNeurovisceral control

·· The major control center for the The major control center for the autonomic nervous system is the autonomic nervous system is the hypothalamus but the medulla and hypothalamus but the medulla and spinal cord are also involved spinal cord are also involved

ANS = parasympathetic + sympathetic ANS = parasympathetic + sympathetic Cell bodies are clumped in ganglia outside Cell bodies are clumped in ganglia outside

the CNS the CNS Parasympathetic ganglia are located near Parasympathetic ganglia are located near

the organ being innervated the organ being innervated Sympathetic ganglia lie close to the spinal Sympathetic ganglia lie close to the spinal

cord and form the sympathetic chain gangliacord and form the sympathetic chain ganglia

·· Chemical and neural feedback loops allow the ANS Chemical and neural feedback loops allow the ANS to maintain internal homeostasis via the control of to maintain internal homeostasis via the control of glands, smooth muscles (blood vessels, digestive glands, smooth muscles (blood vessels, digestive tract), and cardiac muscle tract), and cardiac muscle

The sympathetic and parasympathetic systems act as The sympathetic and parasympathetic systems act as antagonists to each other antagonists to each other

The sympathetic system releases the stimulatory The sympathetic system releases the stimulatory neurotransmitter epinephrine (adrenalin) or neurotransmitter epinephrine (adrenalin) or norepinephrine (noradrenalin) norepinephrine (noradrenalin)

The parasympathetic system invokes an inhibitory The parasympathetic system invokes an inhibitory response releasing acetylcholine into neuroeffector response releasing acetylcholine into neuroeffector junctions junctions

The vagus nerve is particularly important due to its The vagus nerve is particularly important due to its connections with the majority of the internal organsconnections with the majority of the internal organs

Symphatetic and Symphatetic and parasympthathetic parasympthathetic nervous Systemnervous System

Autonomic Nervous Autonomic Nervous SystemSystem

What is Autonomic Nervous What is Autonomic Nervous System?System?

– Functions:Functions: -maintains homeostasis of key visceral function necessary -maintains homeostasis of key visceral function necessary

for lifefor life-provides innervation to heart, blood vessels, visceral -provides innervation to heart, blood vessels, visceral organs, glands and all organs composed of smooth muscleorgans, glands and all organs composed of smooth muscle-regulates activities of these structures which function -regulates activities of these structures which function below level of consciousness (involuntary) below level of consciousness (involuntary)

-contains both central (hypothalamus, medulla oblongata, -contains both central (hypothalamus, medulla oblongata, and spinal cord) and peripheral (pre- and post-ganglionic and spinal cord) and peripheral (pre- and post-ganglionic neurons) portionsneurons) portions-drugs which treat diseases that require modification of -drugs which treat diseases that require modification of autonomic functions act either in peripheral or CNS autonomic functions act either in peripheral or CNS

Organization:Organization:

-consists of 2 neuron systems-consists of 2 neuron systemsa) Preganglionic neurons:a) Preganglionic neurons:

-cell body in spinal cord or brain-cell body in spinal cord or brain-modulated by brain & spinal reflexes-modulated by brain & spinal reflexes-leaves spinal cord & synapses with post--leaves spinal cord & synapses with post-ganglionic neurons in ganglia (relay ganglionic neurons in ganglia (relay centers)centers)

b) Postganglionic neurons:b) Postganglionic neurons:

-sends axons to effector organs-sends axons to effector organs

-most activity takes place at junctions of pre- -most activity takes place at junctions of pre- and post-ganglionic nerves or at neuro-and post-ganglionic nerves or at neuro-effector junctioneffector junction

The Autonomic Nervous The Autonomic Nervous SystemSystem

Components Of NeuronComponents Of Neuron

Nuerotransmitters in the Nuerotransmitters in the Autonomic Nervous Autonomic Nervous SystemSystem

Nerves interact with effector organs by Nerves interact with effector organs by releasing a chemical mediator called a releasing a chemical mediator called a neurotransmitter that diffuses across a small neurotransmitter that diffuses across a small area called the neuroeffector junction which area called the neuroeffector junction which then interacts with a receptor on the effector then interacts with a receptor on the effector organ thereby illiciting a responseorgan thereby illiciting a responseThe nerve terminal is responsible for:The nerve terminal is responsible for:

synthesis synthesis storage storage release release inactivation of the neurotransmitterinactivation of the neurotransmitter

Chemical transmission of nerve impulses Chemical transmission of nerve impulses occurs between:occurs between:

pre and postganglionic neurons pre and postganglionic neurons postganglionic neurons and neuroeffector postganglionic neurons and neuroeffector

organs organs in both sympathetic and parasympathetic in both sympathetic and parasympathetic

divisionsdivisions

Events during neurochemical transmission:Events during neurochemical transmission:– ·· electrical impulses from CNS electrical impulses from CNS

increase in Na+ permeability increase in Na+ permeability local depolarization of neuronal membrane local depolarization of neuronal membrane increase in K+ permeability --> repolarization increase in K+ permeability --> repolarization therefore, ion currents through distinct channels --> action potential therefore, ion currents through distinct channels --> action potential action potential arrives at nerve terminal action potential arrives at nerve terminal release of stored neurotransmitter by exocytosis release of stored neurotransmitter by exocytosis neurotransmitter diffuses across synaptic cleft neurotransmitter diffuses across synaptic cleft interacts with receptor on postganglionic cell body or effector organ interacts with receptor on postganglionic cell body or effector organ alters ion permeability and initiates action potential in post-alters ion permeability and initiates action potential in post-

ganglionic nerve cell body ganglionic nerve cell body or mediates a response in the end-organ (response is dependent on or mediates a response in the end-organ (response is dependent on

transmitter and receptor subtype)transmitter and receptor subtype)

Autonomic PharmacologyAutonomic Pharmacology

Autonomic PharmacologyAutonomic Pharmacology because of chemical transmission, junctions in because of chemical transmission, junctions in

peripheral autonomic motor pathways are a logical peripheral autonomic motor pathways are a logical site for pharmacological manipulation of visceral site for pharmacological manipulation of visceral function.function.

Because neurotransmission involves different Because neurotransmission involves different mechanisms in different segments of the autonomic mechanisms in different segments of the autonomic nervous system, drugs are more or less selective in nervous system, drugs are more or less selective in their actions. For example, local anesthetic drugs their actions. For example, local anesthetic drugs block action potential propagation (common to all block action potential propagation (common to all neurons) and are nonselective. Drugs that act on neurons) and are nonselective. Drugs that act on transmitter synthesis and storage, or those that transmitter synthesis and storage, or those that activate or block receptors are selective because of activate or block receptors are selective because of differences in the cholinergic and adrenergicdifferences in the cholinergic and adrenergic systems.systems.

Cholinergic neurons: synthesize and release Cholinergic neurons: synthesize and release acetylcholine (ACh)acetylcholine (ACh)

Include:Include: All motor fibers to skeletal muscle (nonautonomic) All motor fibers to skeletal muscle (nonautonomic) Preganglionic efferent neurons of both SNS and PNS Preganglionic efferent neurons of both SNS and PNS Postganglionic neurons of PNS Postganglionic neurons of PNS Some postganglionic fibers of SNS Some postganglionic fibers of SNS Adrenergic neurons: synthesize and release Adrenergic neurons: synthesize and release

norepinephrine (NE)norepinephrine (NE) Include:Include: Postganglionic neurons of SNS Postganglionic neurons of SNS Adrenal medulla is a modified sympathetic ganglion Adrenal medulla is a modified sympathetic ganglion ·· It receives sympathetic preganglionic fibres and It receives sympathetic preganglionic fibres and

releases epinephrine (EP) and NEreleases epinephrine (EP) and NE

Adrenergic Nerve terminalAdrenergic Nerve terminal

Biosynthesis And Biosynthesis And Transmission Of Acetyl Transmission Of Acetyl CholineCholine

Biosynthesis and Transmission of Catecholamines NE and EP are catecholamines synthesized from tyrosine

via dopamine NE is retained in storage vesicles Action potential leads to increased intracellular Ca2+ ----

> NE release from vesicles response to NE is terminated by: a) energy dependent amine uptake pump b) simple diffusion into postsynaptic cell after reuptake (uptake 1) NE is deaminated by

monoamine oxidase in mitochondria or sequestered in storage vessels

Chlonergic Receptor TypesChlonergic Receptor Types a) Muscarinic b) Nicotinic Muscarinic Receptors found on plasma membranes of most peripheral visceral organs

innervated by nerves of PNS stimulated by muscarine, an alkaloid from Amanita muscaria parasympathomimetic drugs mimic effects of ACh release at post-

ganglionic nerve endings of PNS effects are blocked by atropine (plant alkaloid) also found on cells stimulated by postganglionic "cholinergic" neurons

of SNS (e.g. sweat glands)

Nicotinic ReceptorsNicotinic Receptors found in synapses in autonomic ganglia of both SNS and found in synapses in autonomic ganglia of both SNS and

PNS PNS found on membranes of skeletal muscle fibers at found on membranes of skeletal muscle fibers at

neuromuscular junction neuromuscular junction stimulated by nicotine stimulated by nicotine nicotinic receptors in ganglia differ from neuromuscular nicotinic receptors in ganglia differ from neuromuscular

junction since blocked by different agonists junction since blocked by different agonists nicotinic agonists --> conformational change in receptor nicotinic agonists --> conformational change in receptor

-->opening of gated ion channel --> Na/K ion diffusion ---->opening of gated ion channel --> Na/K ion diffusion --> depolarization > depolarization

effects blocked by curare (plant poison) at effects blocked by curare (plant poison) at neuromuscular junctionneuromuscular junction

Chlonergic Nervous Chlonergic Nervous TerminalTerminal