anatomy of nervous system

1. Nervous System

2. Nervous system is divided into
2
- Peripheral nervous system
(PNS) and
- Central nervous system
(CNS)

3. Peripheral nervous system (PNS)consists
of cranial nerves and spinal nerves.
PNS relays information to and from the
central nervous system (CNS).

4.  Nerve cells are called
neurons. Axons,
dendrites and cell
bodies are the main
parts of a neuron.
 Axons transmit impulses
away from the cell body
of a neuron
 Dendrites are extensions
which transmit impulses
toward the cell body.

5. SYNAPSE
The small gap between the
axon of one neuron and the
dendrites or cell body of the next
Neuron is called synapse.
Presence of synapse ensure
one-way transmission of impulses.

6. TYPES OF NEURON
Neurons are classified into 3 main groups
Sensory neurons, motor neurons and
interneurons.

7. SENSORY, MOTOR AND INTERNEURON

8.  Motor neuron (efferent neuron) carry
impulses to the effectors (muscles and
glands).
 Motor neuron linked to skeletal muscles are
called somatic neuron.
 Motor neurons linked to smooth muscle,
cardiac muscle and glands are called
visceral.

9. Sensory neurons carry impulses
from receptors to the central nervous
system (afferent neurons)

10.  Sensory and motor neurons make up the
peripheral nervous system .
 Interneurons are found entirely within the
central nervous system. They are arranged
so as to carry only sensory and motor
impulses or to integrate these functions.
Some interneurons in the brain are
concerned with thinking, learning and
memory.

11.  Nerve impulses are action potential which carry
information along the neuron membrane.
 Neurons not carrying an impulse has abundant Na+
ions outside the cell and abundant K+ and negative
charged ions inside.

12. SEQUENCE OF EVENTS IN THE TRANSMISSION OF ACTION
POTENTIAL
Polarisation
 Neuron membrane has a positive charge outside and negative charge inside
 Sodium ions are more abundant outside and potassium and negative ions are more abundant
inside
 Sodium and potassium pump maintain these equilibrium (resting membrane potential) in the
absence of any stimulus.
Depolarisation
1. Stimulus (chemical, electrical or mechanical) alter the resting membrane potential of the neuron
membrane
2. Voltage regulated sodium channels open to permit the influx of sodium ion into the cell
(depolarisation)
3. Inside of the membrane becomes more positive compared to the outside (-60mv to +30mv).
4. Voltage regulated sodium channel closes at +30mv.
Repolarisation
1. Voltage regulated potassium channels are now open and potassium ions flow out of cell
membrane. This results in making the outside more positive than inside.
2. Sodium ions are returned outside and potassium ions returned inside the cell by sodium
potassium pump
3. The voltage regulated potassium channels begin to close at -70mv.

13.  Nerve plexus is a network of neurons from
several segments of the spinal cord that
combine to form nerves to specific parts of
the body.

15. MAJOR PERIPHERAL NERVES
Nerve Spinal nerves that contribute Distribution
Phrenic C3 – C5 Diaphragm
Radial C5 – C8, T1 Skin and muscles of posterior arm, forearm, and
hand, thumb and first 2 fingers
Median C5 – C8, T1 Skin and muscles of anterior arm, forearm and hand
Ulnar C8, T1 Skin and muscles of medial arm, forearm and hand;
little finger and ring finger
Intercostal T2 – T12 Intercostal Muscles, abdominal muscles, skin of
trunk
Femoral L2- L4 Skin and muscles of anterior thigh, medial leg and
foot
Sciatic L4 – S3 Skin and muscles of posterior thigh, leg and foot

16. BRAIN
 Brain is made up of approximately 100 billion
neurons and contains trillions of synapses.
The major parts of the brain are the medulla,
pons, midbrain, (collectively called brain
stem), cerebellum, hypothalamus, thalamus
and the cerebrum.

18.  The four cavities within the brain are called
ventricles . Each ventricle contains a network
of capillaries called choroid plexus, which
forms the cerebrospinal fluid from blood
plasma.

19. MEDULLA
Medulla extends from the spinal cord to the
pons and is anterior to the cerebellum. Medulla
contains
 Cardiac centres that regulate the heart
 Vasomotor centres that regulate the diameter
of blood vessels and thereby blood pressure
 Respiratory centres that regulate breathing

20. PONS
 Pons bulges anteriorly from the upper part of
the medulla. Within the pons are 2
respiratory centres that work with those in
the medulla to produce a normal breathing
rhythm. Cranial nerves V and VIII connect
the brain in the pons.

21. MIDBRAIN
 Midbrain extends from the pons to the
hypothalamus. It encloses the cerebral
aqueduct which is a tunnel that connects the
thrid and fourth ventricles. Visual and
auditory reflexes are integrated in the
midbrain.

22. CEREBELLUM
 Cerebellum is situated inferior to the occipetal lobes of the cerebrum and
is separated from the medulla and pons by the fourth ventricle. Some of
the functions of cerebellum include regulation of muscle tone,
coordination, maintenance of posture and equilibrium.
 Cerebellum uses information about gravity and movement provided by
receptors in the inner ears to regulate equilibrium.

23. HYPOTHALAMUS
Hypothalamus is a small area located superior to the pituitory gland and
inferior to the thalamus. The main functions of hypothalamus are given
below:
 Production of anti-diuretic hormone and oxytocin which are then stored
in the posterior pituitory gland.
 Production of releasing factors which stimulate anterior pituitory gland to
secrete hormones.
 Regulation of body temperature by promoting responses such as
sweating and shivering.
 Regulation of food intake
 Integration of the functioning of the autonomic nervous system
 Simulation of visceral responses during emotional situations.
 Regulation of body rhythms such as secretion of hormones, sleep
cycles, changes in mood or mental alertness

24. THALAMUS
 The thalamus is situated superior to the
hypothalamus and inferior to the cerebrum.
 Many of the functions of the thalamus are
concerned with sensation. The Thalamus
integrates the impulses from the cutaneous
receptors and from the cerebellum. Part of
the information associated with pain are
processed thalamus.

25. CEREBRUM
 Cerebrum is the largest part of the human brain.
It consists of two hemispheres which are
separated by longitudinal fissure. At the base of
the grove this deep groove is the corpus
callosum that connects the right and left
hemispheres. The surface of the cerebrum is
gray matter called the cerebral cortex.
 The cerebral cortex is divided into lobes that
have the same names as the cranial bones
external to them.

26. CEREBRAL HEMISHPHERES

27. BASAL GANGLIA
 These are paired masses of gray matter
within the white matter of cerebral
hemispheres. Their functions are certain
aspects of voluntary movement and they
work with cerebellum. The basal ganglia help
regulate muscle tone, coordinate motor
movements and posture. It also inhibits
unwanted muscular activity.

28. MENINGES
 The connective tissue membrane that covers
the brain and spinal cord are called
meninges.
 Outer layer – Duramater
 Middle layer – arachnoid mater
 Innermost layer – Pia mater

29. CEREBROSPINAL FLUID
 Choroid plexus in the ventricles produce a fluid from blood
plasma called cerebrospinal fluid (CSF).
 Approximately 500ml of CSF is secreted each day, but only
approximately 150mls is in the ventricular system at any one
time.
 Normal CSF pressure is approximately 10mmHg in the
lateral recumbent position.