Download Peripheral nervous system

Physiology
232 BMS
Dr/Nahla Yacout
2016/2017
 Nervous system & its function
 Classification of nervous system
 Brain
Parts of the brain & the function of each part
 Spinal cord & spinal nerves
 Meninges & cerebrospinal fluid
 Peripheral nervous system
Components of PNS
Functional classification of PNS
 Neurons
Structure of neurons
Classification of neurons (Structural & functional)
 Action potential & its steps
 The nervous system is the master controlling & communicating
system of the body
 Every thought, action & emotion reflects its activity
 Its cells communicate by signals, which are rapid & specific, &
usually causes immediate responses
1. It monitors the changes occurring inside & outside the
body………This gathered information is called
(Sensory input)
2. It interprets this sensory input & decides what should be
done at each moment …………… (Integration)
3. It causes a response……………(Motor output)
(By activating effector organs)
Ex:
 When you are driving, & see a red light ……… Sensory
input
 Your nervous system integrates this information (Red
means stop) ……….. Integration
 Your foot will go to the break ……….. Motor output
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Central nervous system
(CNS)
Brain
Spinal cord
Peripheral nervous system
(PNS)
Consists of
the nerves that extend from
the brain (Cranial nerves)
& spinal cord (Spinal nerves)
The brain constitutes about one fiftieth of the body weight &
lies within the cranial cavity
Parts of the brain:
Midbrain
Cerebrum
Pons
(Brain stem)
Cerebellum
Medulla oblongata
Cerebrum:
 Is the largest part of the brain
 Is divided into right & left cerebral hemispheres by longitudinal cerebral
fissure
 Deep in the brain the hemispheres are connected by nerve fibers (White
matter)
 The superficial part of the cerebrum is composed of the nerve cell
bodies (Grey matter)
 Each hemisphere is divided into lobes:
Frontal – Parietal – Temporal - Occipital
Hypothalamus:
Functions:
1. Controls the hormone secretion from pituitary gland
2. Control of appetite & thirst
3. Control of body temperature
Pons
 Is placed infront of the cerebellum, below the midbrain & above the medulla
oblongata
 Pons differ from the cerebrum in that:
 In cerebrum: White matter lies deeply – Grey matter lies on the surface
 In pons: Grey matter lies deeply – White matter lies on the surface
Deep within the hemispheres, there are masses of grey matter,
including, Thalamus & Hypothalamus
Thalamus: Sensory input from the organs is transmitted to thalamus
before reaching the cerebrum
Medulla oblongata:
Extends from the pons above & is continuous with the spinal cord below
It contains the vital centers as:
 Cardiac center
 Respiratory center
 Reflex centers of vomiting, coughing, swallowing
Cerebellum:
 Is placed behind the pons
Functions:
Important in voluntary muscular movement & balance of the body
 Is the elongated, cylindrical part of the central nervous
system, which is placed inside the vertebral canal
 It is surrounded by meninges & cerebrospinal fluid
 There are 31 pairs of spinal nerves, that are named
according to the vertebrae with which they are
associated
8 cervical – 12 thoracic – 5 lumbar – 5 sacral
1 coccygeal
The spinal cord is the link between the brain & the rest of
the body
 Nerves carrying impulses from the brain to various
organs pass though the spinal cord & then they leave the
cord & passes to the organ they supply
 Sensory nerves from the organs to the brain pass
upwards through the spinal cord
Some activities of the spinal cord are independent of the brain, called
(Spinal reflexes)
Consist of three elements:
 Sensory neurons
 Connector neurons
 Motor neurons
Example:
The pain impulse initiated by touching a hot surface with the finger is
transmitted to the spinal cord by sensory nerves
This will stimulate many connector & motor neurons in the spinal cord, which
results in contraction
Are 3 membranes covering the brain & spinal cord
Named from outside to inside:
 Dura matter
 Arachnoid matter
 Pia matter
 Dura & arachnoid matters are separated by space called:
Subdural space
 Arachnoid & pia matters are separated by space called:
Subarachnoid space (This space contains cerebrospinal fluid)
Is a clear fluid that is present in the subarachnoid space
It consists of:
 Water
 Mineral salts
 Proteins
 Glucose
 Urea
 Creatinine
Functions of CSF:
1. Supports & protects the brain & spinal cord
2. It maintains constant pressure around brain & spinal cord
3. It keeps the brain & spinal cord moist
Cranial nerves (12 pairs)
Carry impulses to & from the brain
Spinal nerves
Carry impulses to & from the spinal cord
31 pairs of spinal nerves that are named according to their
point of exit from the spinal cord
Cervical (8 pairs) Thoracic (12 pairs) Lumbar (5 pairs)
Sacral (5 pairs)
Coccygeal (1 pair)
Functional classification of PNS
Sensory (Afferent) division
Consists of nerves that carry impulses to the CNS
from the whole body
Motor (Efferent) division
Consists of nerves that carry impulses from the CNS
to the whole body (Effector organs as: glands,
muscles)
Motor (Efferent) division
Somatic NS (Voluntary)
Consists of somatic motor nerves that conduct impulses
from CNS to skeletal muscles (Voluntary muscles)
Autonomic NS (Involuntary)
Consists of motor nerves that conduct impulses from
CNS to smooth muscles (Involuntary muscles) &
cardiac muscles
Neurons
 They are the structural & functional units of the nervous
system
 They are highly specialized cells that conduct messages
in the form of impulses from one part of the body to
another
Amitotic
Have no ability to divide – no ability to be replaced
if destroyed
Have high metabolic rate
Require continuous supply of nutrients & oxygen
Structure of neurons
1.
2.
3.
4.
Cell body (Soma)
Dendrites (Transfer the messages towards the cell body)
Axon
Myelin sheath (Sheath around neurons to protect them)
Myelinated neurons……..Conduct impulses rapidly
Unmyelinated neurons…….Conduct impulses slowly
Classification of neurons
Structural
Multipolar neurons
Bipolar neurons
Unipolar neurons
Functional
Sensory (Afferent)
Motor (Efferent)
Interneurons
(Association)
Multipolar
Many processes extend from
the cell body
Unipolar
One process extend
from the cell body
Bipolar
Two processes extend
from the cell body
(One fused dendrite,
& the other is an
axon)
Sensory
Transmit impulses from organs
to CNS
Interneurons
Lie between sensory
& motor neurons
Motor
Transmit impulses away
from CNS to the effector organs
(Muscles, glands)
Components of reflex action:
1. Receptor……Site of stimulus action
2. Sensory neuron……Transmits impulses to the CNS
3. Integration center……Is always in CNS
4. Motor neurons…….Transmit impulses from CNS to
effector organs
5. Effector…….Muscles or glands that respond to the
impulses (By contraction or secretion)
Nerve
 Is a part of the peripheral nervous system
 It consists of parallel bundles of axons (Some myelinated
& some not) enclosed by connective tissue
Sensory
Carry impulses to
CNS
Motor
Carry impulses
away from CNS
(to organs)
Mixed
Carry impulses
to & from CNS
Action potential
 Neurons are highly irritable (responsive to stimuli)
 When a neuron is stimulated, an impulse is generated &
conducted along the neuron …….. This response is called
(Action potential)
Membrane ion channels
Membrane contains variety of proteins that act
as ion channels
These ion channels are selective to the type
of ion it allows to pass
Ex: (Potassium ion channel allows only potassium
ions to pass)

When these ion channels open, ions diffuse quickly across
the membrane from area of high concentration to area of low
concentration
Resting membrane potential
Inside the membrane is more negative than outside
(This state is called Resting membrane potential)
Why??????
The membrane is very slightly permeable to
sodium in comparison to potassium
& SO…..Potassium ions diffuse out of the cell more easily
than sodium ions can enter the cell
& SO……The easy flow of potassium out of the cell
causes the cell to become more negative inside than
outside
Depolarization
Inside of the membrane
becomes less negative
Hyperpolarization
Inside of the membrane
becomes more negative
1. Resting state:
Na+ & K+ channels are closed
2. Depolarization:
Na+ channels open & K+ channels still closed
& so……Na+ ions will rush inside the cell ……. Leading to
more +ve charge inside
3. Repolarization:
Na+ entry will decline …… K+ channels will open & K+
rush out of the cell …… & so negativity inside the
membrane will be restored
4. Na+ K+ pump
The ion redistribution will be accomplished by SodiumPotassium pump (Will take K+ ions inside & Na+ ions
outside)
This action potential will be propagated along the
entire axon