NERVOUS SYSTEM

TABLE OF CONTENTS

INTRODUCTION

•Nervous system is the chief controlling and coordinating system of the body.

•It control and regulates all activities of the body, whether voluntary or involuntary.

•This is based on the special properties:-

  1. Sensitivity
  2. Conductivity
  3. Responsiveness

GENERAL FUNCTION OF THE NERVOUS SYSTEM

Sensory: –

The sensory impulses are transmitted by the sensory (afferent) nerves from periphery (skin, mucous membranes, muscles, tendons, joints, and special sense organs) to the central nervous system (CNS).

Motor: –

The motor impulses are transmitted by the motor (efferent) nerves from the central nervous system to the periphery (muscle and glands)

ANATOMICAL CLASSIFICATION OF NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM

•The central nervous system (CNS) is composed of the brain and spinal cord. 

•These neurons cannot regenerate if damaged.

PERIPHERAL NERVOUS SYSTEM

•(PNS) is made up of peripheral nerves that connect the CNS to the rest of the body. 

•These neurons can regenerate if damaged.

•12 pairs of cranial nerves.

•31 pairs of spinal nerves.

PNS can be subdivided into 2 divisions:

(1)  Somatic

•Cranial & spinal nerves connecting CNS to skin & skeletal muscles

•Oversees conscious activities

(2)  Autonomic

•Cranial & spinal nerves connecting CNS to heart, stomach, intestines, glands.

•It controls unconscious activities.

ANS divided into 2 part:-

  1. Sympathetic: – Acts in emergency
  2. Parasympathetic: -Counter acts the sympathetic ns after the emergency.
PARASYMPATHETICSYMPATHETIC
•Decreases heart rate, bronchiole dilation, blood glucose, blood to skeletal muscle•Decreases digestion, pupil size, urinary output
•Increases digestion, pupil size, urinary output•Increases heart rate, bronchiole dilation, blood glucose, blood to skeletal muscle
•“rest and digest”•“fight or flight”

PARASYMPATHETIC vs SYMPATHETIC DIVISIONS

CELL TYPE OF NERVOUS TISSUE

•Nervous Tissue is composed of two major cell types: neurons and neuroglial cells.

NEURONS

•The neurons are the structural and functional units of the nervous system.

•The two main properties of neurons are excitability and conductivity.

•Neurons are made up of a cell body, dendrites, and axons. 

•Cell Body consists of a mass of cytoplasm surrounded by a plasma membrane. It contains a large vesicular nucleus with prominent nucleous.

•Dendrites receive information. It bring impulses towards the cell body, hence they often branch profusely to increase the reception area of the neurons.

•Axons send information. Single long process.

•It does not branch except at its termination to form terminal boutons.

•Larger axons are enclosed by sheaths of myelin produced by Schwann cells.  

•Narrow gaps in the myelin sheath between Schwann cells are called nodes of Ranvier.

STRUCTURAL CLASSIFICATION OF NEURONS

(1) Multipolar

  • Many processes arising from cell body
  • Brain or spinal cord

(2) Bipolar

  • 2 processes (1 from each end of cell body)
  • Ear, eyes, nose

(3) Unipolar

  • Single process extends from cell body
  • Outside of brain & spinal cord

FUNCTIONAL CLASSIFICATION OF NEURONS

Sensory Neurons – (afferent) have specialized receptor ends that sense stimuli and then carry impulses from peripheral body parts to brain or spinal cord. Can be unipolar or bipolar.

Interneuronslie entirely within the brain or spinal cord; direct incoming sensory impulses to appropriate parts for processing and interpreting.

Motor Neurons – (efferent) carry impulses out of the brain or spinal cord to effectors (muscles, glands). 

Interneurons and motor neurons are multipolar.

NEUROGLIAL CELL

•Provide physical support, insulation (myelin), and nutrients for neurons.

•All glial cells are much smaller but far more numerous than the nerve cells.

(a)Astrocytes: these are the largest and most numerous.

The astrocytes are star-shaped with many dendrite-like processes whose ends possess small swellings called foot processes.

The foot processes form sleeve around the capillary. The sleeve along with endothelial wall of the capillary forms the blood-brain barrier.

The astrocytes are of two types;

Protoplasmic found in gray matter & fibrous found in white matter

(b) Oligodendrocytes: these are smaller than astrocytes and as the suggests, have fewer processes.

Oligodendrocytes form myeline sheath around the fibers of CNS.

(c) Ependymal Cells: these cells line the ventricles of brain and the central canal of spinal cord.

(d) Microglia: these are the smallest glial cells. These are phagocytic cell derived from mesoderm.

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