Nervous System Parts of Nervous System Central Nervous

Nervous System

Parts of Nervous System • Central Nervous • Peripheral Nervous System • 1 - Cerebrospinal • 1 - Brain nervous system(12 • 2 -Spinal cord CNs, 31 SNs) • 2 - Peripheral Autonomic Nervous System

Base of the Brain.

Lateral surface of brain.

Cross section of spinal cord.

Cranial nerves.

• Spinal nerves & formation of • Cervical plexus • Brachial plexus • Lumbar plexus • Sacral plexus

Spinal Nerves • 31 nerves connecting the spinal cord and various body regions. • 8 paired cervical nerves • 12 paired thoracic nerves • 5 paired lumbar nerves • 5 paired sacral nerves • 1 pair of coccygeal nerves

Spinal Nerves • The 2 roots join to form a spinal nerve prior to exiting the vertebral column. • Roots are short and horizontal in the cervical and thoracic regions while they are longer and more horizontal in the sacral and lumbar regions. • Almost immediately after emerging from its intervertebral foramen, a spinal nerve will divide into a dorsal ramus, a ventral ramus, and a meningeal branch that reenters and innervates the meninges and associated blood vessels.

Cells of Nervous System • 1 - Neurons: Excitable cells • 2 - Supporting cells: Non-excitable cells (Neuroglia & Ependyma and Schwann cells) Neuroglia Neuron

Neuron • 1 - Cell body • 2 - Cell processes- Dendrites and Axon • Types of neurons (According to number of processes) a- Unipolar, eg: mesencephalic nucleus b- Pseudo-unipolar, eg: sensory ganglia c- Bipolar, eg: vestibular ganglia d- Multipolar, eg: most common (According to length of axon- Golgi type 1 &2)

Neuron.

Types of neurons.

Neuroglia • • • 2 - Ependymal cells 3 - Capsular or satellite cells 4 - Schwann cells 5 - Different types of supporting cells Neuroglial cells are : Astrocytes, Oligodendrocytes, Glioblasts, Microglia.

Functions of glial & ependymal cells • • 1 - Support to neurons 2 - Insulation 3 - Phagocytosis 4 - Repair of damaged areas 5 - Storing of neurotransmitters 6 - Oligodendrocytes myelinate tracts 7 - Ependymal cells concerned with blood - brain barrier.

Reflex arc • It is the basic functional unit of the nervous system. • A simple arc made up of a- a receptor b- a sensory or afferent neuron c- a motor or efferent neuron d- an effector

Reflex Arcs • A reflex is a rapid, predictable motor response to a stimulus. Unlearned and involuntary. • Example? • Components of a reflex arc: – Receptor site of stimulus – Sensory neuron transmits afferent info to CNS – Integration center 1 or more interneurons – Motor neuron transmits efferent signals to effector – Effector muscle or gland

Nerves • Peripheral nerves • Spinal nerves -31 pairs 8 - cervical 12 -thoracic 5 -lumbar 5 -sacral 1 -coccygeal • Nerve plexuses

Nerve fibers • Nerve fibre is an axon with its covering of myelin sheath. Myelinated fibers. • Thinner axons (less then 1 micron) do not have the myelin sheth. Nonnyelinated fibres. • Both will have a neurolemmal sheath, but tracts wont have it.

Myelin sheath formation.

Classification of Peripheral nerve fibres • According to function, 1 - Somatic efferent 2 - General vicseral efferent 3 - Special vicseral efferent 4 - General somatic afferent 5 - General vicseral afferent 6 - Special vicseral afferent 7 - Special somatic afferent

Classification of Peripheral nerve fibres • According to Size & speed of conduction, 1 - Group A fibres: Thick and fast 2 - Group B fibres: Medium size and speed 3 - Group C fibres: Thinnest and slowest Degeneration and Regeneration of Neurons (Wallerian Degeneration)

Autonomic nervous system • It controls the involuntary activities of the body. • It is having a) Preganglionic fibres, b) The ganglia, c) Postganglionic fibres • Two types 1 - Sympathetic system 2 -Parasympathetic system

• Autono mic nervous system.

• Multipolar motor neuron. • Section of spinal cord. • Diagram of spinal cord with anterior & posterior root.

Sympathetic system • 1 - It is known as thoracolumbar out flow (T 1 to L 2 segment) • 2 - Preganglionic fibres (medulleted-white rami communicantes) arise from lateral column of spinal cord, emerge through ventral rami and connected to the ganglia of sympathetic chain. • 3 - From the ganglia postganglionic fibres (nonmedullated-grey rami communicantes) run for some distancebefore reaching the organ of supply.

• 4 - Sympathetic nerve endings are adrenergic in nature (noradrenalinneurotransmetre) • 5 - Functionally sympathetic nerves are vasomotor, stimulation leads to increased blood supply to skeletal muscles, heart and brain. Also causes dilation of pupil, pale face, dry mouth, tachycardia, rise in blood pressure, inhibition of hollow viscera, and closure of peripheral sphincters. • By this deals with emergencies or emotional crises.

Parasymapathetic system • 1 - It is known as craniosacral out flow (brain-3 rd, 7 th, 9 th and 10 th CNs and S 2 -4 segment) • 2 - Preganglionic fibres are very long, reaching up to the viscera of supply. The ganglia situated on or near the viscera, therefore postganglionic fibres are very short • 3 - Parasympatetic nerve endings are cholinergic in nature • 4 - Functionally, parasympathetic activity is seen when the subject is fully relaxed. It leads constricted pupil, flushed face, moist mouth, slow pulse, low blood pressure, contraction of bladder and gut and relaxing of peripheral sphincters.

Applied anatomy • 1. Irritation of motor nerve causes muscular spasm and sensory nerve causes tingling, numbness and pain over the area of distribution. • 2 -Damage to a motor nerve causes muscular paralysis and sensory nerve causes anaesthesia and analgesia. • 3 - Severe pain along the distribution of anerve is neuralgia. Inflammation is neuritis. • 4 - Denervation leads to tropic changes in the skin.