The nervous system ا. د : خالد نعيم حمدي Prof.Khaled Naiem

The nervous system (N.S ) regulates all the body functions. Sensory function Motor function Interpretation

The (N.S) is formed of 2 system : The central nervous system ( C.N.S ) . The peripheral nervous system ( P.N.S ) . + The autonomic nervous system ( A.N.S )

The ( C . N . S ) : Includes the brain + spinal cord .The brain is made up of : .Cerebrum .Cerebellum .Brain Stem

The ( p . N . S ) : The P.N.S is formed of : . 12 pairs of cranial nerves . 31 pairs of spinal nerves & their ganglia most of the spinal nerves are mixed nerves i.e. motor & sensory

The nerve cell : the neuron The neuron is the functional , structural & embryolgical unit of the nervous system

Neurons Humans have about 100 billion neurons in their brain alone. While variable in size and shape, all neurons have three parts. Dendrites receive information from another cell and transmit the message to the cell body. The cell body contains the nucleus & organelles except the centrioles is absent . The axon conducts messages away from the cell body

The glial cells The glial cells are the supporting cells to the neurons . The glial cells can divide .

Synapses The junction between a nerve cell and another cell is called a synapse. Messages travel within the neuron as an electrical action potential. The space between two cells is known as the synaptic cleft. To cross the synaptic cleft requires the actions of neurotransmitters. Neurotransmitters are stored in small synaptic vessicles clustered at the tip of the axon.

Types of Neurons Three types of neurons occur. Sensory neurons typically have a long dendrite and short axon, and carry messages from sensory receptors to the central nervous system. Motor neurons have a long axon and short dendrites and transmit messages from the central nervous system to the muscles (or to glands). Interneurons are found only in the central nervous system where they connect neuron to neuron.

the brain is made up of : 3 anatomical parts 1) cerebrum 2) cerebellum . 3) brain stem .

The cerebrum The cerebrum is formed off 2 cerebral hemispheres . It forms the largest part of the brain, occupying the anterior and middle cranial fossae in the skull and extending backwards over the tentorium cerebelli. They are made up of superficial layer of nerve cells ( cerebral cortex ) , the basal ganglia within tracts of synaptic connections, and the ventricles containing CSF inside

The cerebrum consisted of: 2 cerebral hemispheres : right and left . .Each hemisphere controls the activities of the opposite side of the body . .The corpus callosum connects the 2 hemispheres anatomically & physiologically

Lobes of the hemispere Each hemisphere is divided into 4 lobes : 1) frontal lobe . 2) Parietal lobe . 3) Occipital lobe . 4) Temporal lobe .

Lies anterior contains most the motor areas + memory + personality The frontal lobe : Lies anterior contains most the motor areas + memory + personality

Lies superior contains most of the sensory areas & emotions . The parietal lobe : Lies superior contains most of the sensory areas & emotions .

Lies posterior and contains the centers of visions . The occipital lobe : Lies posterior and contains the centers of visions .

Lies inferior and contains the centers of hearing & smell . The temporal lobe : Lies inferior and contains the centers of hearing & smell .

The Cerebellum It is formed of 2 cerebllar hemispheres . Controls : 1) Equilibrium 2) Coordination . 3) Muscle tone .

Thr cerebellum The cerebellum is a large structure at the back of the brain, immediately behind the brainstem and below the occipital cortex. The cerebellum receives direct inputs from the sensory fibers in the spinal cord as well as indirect inputs from the motor cortex, possibly as a copy of the commands being sent downward to the spinal cord.

Histology of the brain

The brain stem

The Brain stem Is formed of 3 parts : 1) Midbrain . 2) Pons . 3) Medulle .

The midbrain The midbrain (mesencephalon) occupies only a small region in humans , about 2cm length . The midbrain gives origin to 3rd & 4th cranial nerves . The midbrain contains the reticular formation , substantia nigra & the ventral tegmental area .

The reticular Formation the reticular formation: collects input from higher brain centers and send them to motor neurons . The reticular formation presents in the brain stem

The Substantia Nigra The substantia nigra: helps "smooth" out body movements; damage to the substantia nigra causes Parkinson's disease . The substantia nigra presents in the midbrain .

VTA the ventral tegmental area (VTA): packed with dopamine-releasing neurons . The VTA lies within the midbrain .

The pons The pons seems to serve as a relay station carrying signals from various parts of the cerebral cortex to the cerebellum . The 5th ,6th , 7th & 8th cranial nerves Originate from the pons

The medulla Oblongata The medulla looks like a swollen tip to the spinal cord. The medulla ends commonly at the foramen magnum. The medulla is about 3.5cm length. The back of the medulla & the pons are separated from the cerebellum by a cavity known as the 4th ventricle .

Medulla The vital centers that controls respiration , circulation & blood pressure are present in the brain stem, mainly the medulla oblongata. The last 4 cranial nerves originate from the medulla.

The Blood Supply of the Brain Food and oxygen are carried to the brain by many blood vessels. These vessels are found on the surface of the brain and deep within the brain. The blood vessels (and nerves) enter the brain through holes in the skull called foramina .

Blood Supply Of The Brain Although the brain is only about 2% of the total body weight in humans, it receives 15-20% of the body's blood supply. Because brain cells will die if the supply of blood which carries oxygen is stopped, the brain has top priority for the blood. Even if other organs need blood, the body attempts to supply the brain with a constant flow of blood