Peripheral nerve system

Peripheral nerves system
Prep: Amen Ullah BS Surgical
KMU-IPMS

Functions of Neurons
A nerve cell, is an electrically excitable cell that receives, processes, and transmits information
through electrical and chemical signals.
These signals between neurons occur via specialized connections called synapses.

Peripheral Nervous System
The peripheral nervous system (PNS) is the part of the nervous
system that consists of the nerves and ganglia outside of the brain
and spinal cord.
The main function of the PNS is to connect the central nervous
system (CNS) to the limbs and organs, essentially serving as a
communication relay going back and forth between the brain and
spinal cord with the rest of the body.
Unlike the CNS, the PNS is not protected by the bone of spine and
skull, or by the blood–brain barrier, which makes it prone
to toxins and mechanical injuries.

PNS
Somatic nervous system
The somatic nervous system is part of the peripheral nervous system,
which is the entire nervous system outside of the brain and spinal cord.
The somatic nervous system processes sensory information and controls all
voluntary muscular systems within the body, with the exception of reflex
arcs.
The somatic nervous system, or voluntary nervous system, is that part of
the peripheral nervous system that regulates body movement through
control of skeletal (voluntary) muscles and also relates the organism with
the environment through the reception of external stimuli, such as through
the senses of vision, hearing, taste, and smell.
The somatic nervous system controls such voluntary actions as walking and
smiling through the use of efferent motor nerves,

PNS
Autonomic nervous system:
 The Autonomic nervous system is an involuntary control of smooth
muscle.
The autonomic nervous system is responsible for maintenance
functions (metabolism, cardiovascular activity, temperature
regulation, digestion) that have a reputation for being outside of
conscious control.
It consists of nerves in cardiac muscle, smooth muscle, and exocrine
and endocrine glands.

Reflex arcs
A reflex arc is an automatic reaction that allows an organism to
protect itself reflexively when an imminent danger is perceived.
In response to certain stimuli, such as touching a hot surface, these
reflexes are "hard wired" through the spinal cord.
A reflexive impulse travels up afferent nerves, through a spinal
interneuron, and back down appropriate efferent nerves.

Autonomic Nervous System
The autonomic nervous system is further divided into the following:
Sympathetic nervous system:
The sympathetic division emerges from the spinal cord in
the thoracic and lumbar areas, terminating around L2-3.
Parasympathetic nervous system:
The parasympathetic division has craniosacral “outflow”, meaning that the neurons
begin at the cranial nerves (specifically the oculomotor nerve, facial
nerve, glossopharyngeal nerve and vagus nerve) and sacral (S2-S4) spinal cord.

Sympathetic vs parasympathetic

Sympathetic Nervous System
Promotes a fight-or-flight response, corresponds with arousal and energy generation, and
inhibits digestion.
Diverts blood flow away from the gastro-intestinal (GI) tract and skin via vasoconstriction.
Blood flow to skeletal muscles and the lungs is enhanced (by as much as 1200% in the
case of skeletal muscles).
Dilates bronchioles of the lung through circulating epinephrine, which allows for greater
alveolar oxygenenation.
Increases heart rate and the contractility of cardiac cells, thereby providing a mechanism
for enhanced blood flow to skeletal muscles.
Dilates pupils and relaxes the ciliary muscle of the lens, allowing more light to enter the
eye and enhances far vision.
Provides vasodilation for the coronary vessels of the heart.
Constricts all the intestinal sphincters and the urinary sphincter.
Inhibits peristalsis.
Stimulates orgasm.

Parasympathetic System
The PNS has been said to promote a "rest and digest" or “feed and breed” response,
promotes calming of the nerves return to regular function, and enhancing digestion.
Functions of nerves within the parasympathetic nervous system include:
Dilating blood vessels leading to the GI tract, increasing blood flow (this is important
following the consumption of food).
Constricting the bronchiolar diameter when the need for oxygen has diminished.
Dedicated cardiac branches of the vagus and thoracic spinal accessory nerves impart
parasympathetic control of the heart.
Constriction of the pupil and contraction of the ciliary muscles,
facilitating accommodation and allowing for closer vision.
Stimulating salivary gland secretion, and accelerates peristalsis, mediating digestion of
food and, indirectly, the absorption of nutrients
Nerves of the peripheral nervous system are involved in the erection of genital tissues via
the pelvic splanchnic nerves. They are also responsible for stimulating sexual arousal.

Ventricles of Brain
These are CSF filled cavities in the brain.
There are 4 ventricles whose location are as follows:
The two lateral ventricles- found in each cerebrum.
The third ventricle- in the center of the thalamus and hypothalamus.
The fourth ventricle- located at the base of the cerebellum.
These ventricles are linked to one another by means of small
aqueducts.

Meninges
These are 3 connective tissue layers surrounding the brain and spinal cord and are
collectively called as Meninges. The different layers are as following:
Dura Mater- Superficial, thickest layer. The area above the dura mater is called epidural space
Arachnoid- second layer, thin and wispy.
Pia Mater- the deepest layer, adhered to the brain and spinal cord substance.
Cerebrospinal fluid is located in the subarachnoid space between the arachnoid mater and the pia
mater.
The primary function of the meninges is to protect the central nervous system. In this space, blood
vessels are also found.

Cerebrospinal Fluid
CSF is a clear, colorless body fluid found in the brain and spine.
It is produced in the choroid plexuses of the ventricles of the brain.
It acts as a cushion or buffer for the brain's cortex, providing basic
mechanical and immunological protection to the brain inside
the skull.
The CSF also serves a vital function in cerebral
autoregulation of cerebral blood flow.
Other functions of CSF include, protection, chemical stability,
prevention of brain ischemia and clearance of wastes.
Normally the subarachnoid space contains 135-150 ml of CSF in it.

Peripheral nerve system

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Peripheral nerve system