Nervous System

Nervous System – General Anatomy

Q. Enumerate the :

  1. functions of nervous system
  2. parts of nervous system

A.  1.   Functions of nervous system:

  • Gathers information both from the outside world and from inside the body- SENSORY FUNCTION
  • Transmits the information to the processing area of the brain and spinal cord –TRANSMISSION
  • Processes the information to determine the best response- INTEGRATIVE FUNCTION
  • Sends information to muscles, glands, and organs (effectors) for muscular contraction and glandular secretion – MOTOR FUNCTION

     2. Parts of nervous system :

Nervous system is divided into:

  •  Central nervous system(CNS) – consists of
    • brain and
    • spinal cord
  • Peripheral nervous system (PNS) – consists of
    • 12 pairs of cranial nerves
    • 31 pairs of spinal nerves

central and peripheral nervous system

Q.  Draw a flow chart to show the various subdivisions of  nervous system.

subdivisions of nervous system

 

Q. Draw a labelled diagram to show parts and structure of a neuron.

parts and structure of a neuron

Q. Enumerate the :

  1. types of neurons with examples
  2. types of neuroglial cells and their function

3. Types of neurons:

  • According to the shape and number of processes:
    • Unipolar (pseudounipolar) neuron : single process from the cell body which divides to form dendrite and axon. e.g. dorsal root ganglion cells of the spinal cord.
    • Bipolar neuron:  two processes arise from the cell body , one on each pole. One of them is dendrite , the other axon.  g.  bipolar neurons neurons in the retina , olfactory epithelium and vestibulochochlear ganglia.
    • Multipolar neuron : several dendrites and one axon arise from the cell body. e.g. pyramidal cells of cerebral cortex, motor neurons of anterior horn of spinal cord.

types of neurons

 

  • According to the functions:
    • Sensory or afferent neuron: neurons that transmit impulses from a sensory receptor to the CNS. e.g. dorsal root ganglion cells of spinal cord.
    • Motor or efferent neurons : neurons that transmit impulses from the CNS to an effector organ (muscle or gland). e.g. pyramidal cells of cerebral cortex.

    afferent and efferent neurons

4. Types of neuroglia:

  • Neuroglia in CNS:
    • Asrtocytes : Are star shaped with many processes whose ends called foot processes cover the capillaries to form blood – brain barrier. Astrocytes are of two types:
      1. Protoplasmic astrocytes
      2. Fibrous astrocytes
    • Oligodendrocytes : Are smaller than astrocytes with fewer processes. Form myelin around the axons in CNS.
    • Microglia: Are the smallest glial cells. They phagocytize pathogens and cell debris within the CNS.
    • Ependymal cells: They line the ventricles of brain and central canal of spinal cord. Produce cerebrospinal fluid.

Glial cells

  • Neuroglia in PNS:
    • Schwann cells: Surround the axons of peripheral nerves and form myelin sheath around these nerve fibers.
    • Satellite(capsular) cells:they surround the cell bodies of neurons in the autonomic and sensory ganglia and provide support to them.

schwann cell and satellite cell

All neuroglial cells develop from neural crest except microglia which develops from mesoderm.


Q. Draw labeled diagram of a t
ypical spinal nerve.

typical spinal nerve

 

Q. Define the following:

  1. Neurilemmal sheath
  2. Myelin sheath
  3. Ganglion
  4. Nucleus
  5. Tract

A. 1. Neurilemmal sheath: It is the outer cell membrane of Schwann cells. Beneath the  membrane lies a thin  layer of cytoplasm of Schwann cell and its nucleus.It is present only in the PNS.

2. Myelin sheath: It is a laminated sheath made up of lipoproteins. Its outer surface is encased in neurilemmal sheath. It is interrupted at the nodes of Ranvier.  In case of peripheral nerves the myelin sheath is formed by the Schwann cells and in the central nervous system the sheath is derived from oligodendrocytes. Its functions are:

  • Protects and insulates the nerve fibres.
  • It also increases the rate of conduction of nerve inpulse ( salutatory conduction.

myelinated and unmyelinated nerve fibre

       All  myelinated and non-myelinated  nerve fibres in PNS are surrounded by the  neurilemmal sheath but only myelinated fiberes are surrounded by  myelin sheath. Axons less than 2µm in diameter are unmyelinated


Q. When does myelination begins?

Ans. Myelination begins as early as fourth month of fetal life.

 Q. Name the parts of an axon where myelin sheath is absent.

Ans. The following sites are devoid of myelin sheath:

  • Nodes Of Ranvier ( Gaps of exposed axon between the adjacent Schwann  cells).
  • Proximal part of the axon, close to the cell body.
  • Near the termination of axon before it divides

Q. Can a non-myelinated nerve regenerate?

Ans. A non-myelinated nerve also possesses neurilemmal sheath which is essential for regenearation, therefore it can regenerate.

Q. Define the following:

  1. Nerve
  2. Fiber tract
  3. Ganglion
  4. Nucleus

Ans   1. Nerve:  Is a collection of  axons outside  the CNS

         2. Fiber Tract:  Is a collection of  axons within the CNS.

         3. Ganglion :  Is a collection of nerve cell bodies outside the CNS.

         4. Nucleus: Is a collection of nerve cell bodies within the CNS.

Q. Define synapse and give morphological classification.

Ans. The  junction between two neurons across which the nerve impulse passes from one neuron to another is called synapse.

  • There is no physical contact between two neurons
  • Presynaptic axon ends in a bulb-like structure (boutons terminaux).
  • There is a space, the synaptic cleft, between the presynaptic & the postsynaptic neuron 20-30nm.
  • The end bulb contains synaptic vesicles that release Neurotransmitters.
  • These can either stimulate or inhibit the postsynaptic neuron.

synapse anatomy

Morphological classification of synapses:

  • Axo-dendritic ( commonest)
  • Axo-somatic
  • Axo-axonic
  • Dendro-dendritic
  • Dendro-somatic
  • Dendro-axonic

types of synapses

 

Q. Enumerate the differences between the sympathetic and parasympathetic nervous system. 

 Sympathetic nervous systemParasympathetic nervous system
Origin of nervesThoraclumbarCraniosacral
Length of pre-ganglionic fibersLongShort
Length of post ganglionic fibres ShortLong
Position of ganglionAway from the organNear the organ
NeurotransmitterAcetylcholine and Epinephrine. & Nor epinephrine. Acetylcholine

 

preganglionic and postganglionic fibers of sympathetic and parasympathetic system


Q. What is the action of sympathetic and parasympathetic nervous system on various tissues/organs.

 A.   Action of Sympathetic and parasympathetic nervous system 

Sympathetic nervous systemParasympathetic nervous system
Is involved in fight, fright or flight reactions.Conserves body energy
Involved in ‘E’ activities-Exercise, Emergency, Excitement, Embarressment.Involved in ‘D’ activities- Digestion , Defeacation, Diuresis
Increases heart rate Heart rate decreased
Raises blood pressureBlood pressure decreased
Dilation of bronchi, increases respiratory rateConstriction of bronchi, decreases respiratory rate
Dilates pupilPupils are constricted
Suppresses peristaltic movements of intestines Stimulates peristaltic movements of intestines
Increase ssweat secretion
Constriction of blood vessels

action of sympathetic and parasympathetic nervous system

 

 Q. Give anatomical basis of referred pain.

A.  The pain arising from diseased viscera is referred to the skin which is innervated by the same spinal segment/s that supply the diseased viscera. e.g. gall bladder pain is  referred to  right shoulder tip and pain in appendicitis is referred to umbilicus.

referred pain

Q. Enumerate the differences between the upper motor neuron and lower motor neuron paralysis.

Upper and lower motor neurons

 

A. Differences between upper motor neuron and lower motor neuron paralysis are :

Features Upper motor neuron paralysis (UMN )Lower motor neuron paralysis (LMN)
Paralysis typeSpasticFlaccid
Muscle toneIncreasedDecreased
Muscle atrophyAbsentPresent
Tendon reflexesExaggeratedDiminished
Babinski’s signPresentAbsent
Affected side Usually ContralateralIpsilateral

                                    Babinski’s sign : Dorsiflexion of great toe with fanning of lateral toes on  scratching lateral aspect of plantar surface of foot.

( Normal : Plantar flexion of toes)

Babinski's sign

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