Structure of Spinal Cord | Biology for JAMB PDF Download

SPINAL CORD

• Medulla oblongata comes out from foramen of magnum & continues in neural canal of vertebral column, the continued part of MO is known as Spinal cord. It extends from base of skull to lower vertebra of lumbar. (L1)
• Its upper part is wide while lower most part is narrow known as conus-medullaris.
• Conus medullaris present upto L1 vertebra.
• Terminal part of conus medullaris extend in the form of thread like structure made up of fibrous connective tissue called filum terminale.
• Filum terminale is non-nervous part Metacoel also continues in spinal cord where it is  known as neurocoel or central canal.
• Spinal cord is also covered by Duramater, Arachnoid & piamater. A narrow space is found between vertebra & duramater known as Epidural space.
• Length of spinal cord is 45 cm.
• Length of filum terminale is 20 cm.
• Weight of spinal cord is approximately 35 gm

• The outer-part of spinal cord is of white matter while inner-part contain gray matter.
• On the dorso-lateral & ventro-lateral surface of spinal cord, the gray matter (butter fly like) projects outside & forms the one pair dorsal & ventral horn.
• Due to formation of dorsal & ventral horn white matter is divided in 4 segments & segment is known as Funiculus or white column. 
• Dorsal & ventral horn continue in a tube like (bundle of never fibres) structure known as root of Dorsal & Ventral Horn. In root of dorsal  horn, ganglia is present called Dorsal root ganglia 
• Both root are combined with each other at the place of Intervertebral foramen.
• Sensory neurons are found in the dorsal root ganglia which is pseudounipolar in nature & near to intervertebral  foramen. Its axon extend & gets embedded into gray matter of spinal cord & sensory nerve fibre come from ganglia & make synapse with ventral root neuron.
• Motor neurons are found in the ventral root. Cyton is found in ventral horn while its dendrons are embedded into gray matter of spinal cord where they make synapse with axon of sensory neuron.
• Axon of motor neuron extends upto intervertbral foramen.
• Both sensory & motor nerve fibers combindly come out from intervertebral foramen & form spinal nerve.
• In some part of spinal cord on both side lateral horns are also found. Lateral horn cells are found in these horn.
• There nerve fibre come through ventral root & further come into intervertebral foramen. These fibre called Ramus communicans.
• The group of spinal nerve at the terminal end (L1) of spinal cord form tail like structure called cauda equina (horse tail).
• Ramus communicans forms AND. 
• Spinal nerve & its branches are mixed type except Ramus communicans.

Functions of spinal cord :-

(1) It acts as bridge between brain & organs of the body.

(2) It also provides relay path for the impulses coming from brain

(3) Spinal cord regulates and conducts the reflex action.

Table of Nervous Control of Visceral Organs

SPECIAL POINTS

1. In the brain of frog only 2 meninges are present. The middle meninge that is the Arachnoid is absent.
2. In rabbit, man and mammals- 3 meninges are present.
3. Increase in the amount of cerebro- spinal fluid is a diseased condition termed as the Hydrocephalus 
4. "Meningitis". It arises due to infection or inflammation or injury in the meninges. Infection may be due to virus or bacteria or both.
5. Piamater is the most vascular and conducting and provides nutrition.
6. The power of regeneration is very less in a neuron.
7. The optic lobes of frog are hollow and in them optocoel cavity is found.
8. In frog, 2 optic - lobes are present. These are hollow and termed as Corpora- bigemina. In mammals, 4 solid optic - lobes are present.
9. Around the brain of fishes, only one menix is found called "Menix- primitiva".
10. The valve of vieussens joins the optic- lobes with the cerebellum.
11. Cerebral - cortex is made up of gray - matter and is divided into 3 areas:-
    • Sensory area
    • Motor area.
    • Associated area
12. The sensory and associated areas determine the shape, colour, sound, taste and smell of any object.
13. Motor area regulates muscular - contraction.
14. Broca's area:- It is known as motor speech area.
15. Broca's area is present in the lateral part of the frontal- lobe of the cerebrum. This area translates the written words into speech.
16. If Broca's area  gets destroyed the animal becomes unable to speak.
17. The temporal- lobes of cerebrum regulates the mechanism of hearing.
18. Cerebrum is the centre of following:-
    • Intelligence
    • Emotion
    • Will- power
    • Memory
    • Consciousness
    • Experience
    • Knowledge
    • Voluntary control
    • Laughing and weeping
    • Defecation and micturition.
19. Diencephalon is the centre of carbohydrate - metabolism and fat- metabolism.
20. In rabbit , "Swammerdam's glands " are absent. These glands are present at the origin place of spinal -nerves in vertebrates & present in frog. It provide extra supply of Ca++ for synaptic transmission.
21. Cerebellum made up of three layers and In the middle of cerebellum of brain lobes of flask- shaped cells are found called the "Purkinje- cells".
22. In the nerve- cells , " centrosome" are absent so once formed in development, the nerve-cells do not divide and remain in Inter- phase stage throughout their life ; and grow in size with the growth of the body.
23. The velocity of nerve- impulse is 5 to 50 times more faster in Myelinated nerve - fibres than in Non- myelinated nerve -fibres.
24. In mammals the speed of nerve impulse is 100 - 130 m/sec (maximum). In frog, the speed of nerve impulse is 30 m/sec. In reptiles the speed is 15 to 35 m/sec.
25. Acetylcholinesterase enzyme helps in the dissociation of Acetylcholine.
26. In the form of inhibitory neuro- hormons, - GABA is present. GABA- gamma amino butyric -acid.
27. Acetylcholine is synthesized by the Mitochondria.
28. For the conduction of nerve- impulses, Na+ is necessary.
29. The marking of brain- waves is done through E. E. G i.e Electro- encephalo gram.
30. In embryonal - stages inside the brain the layer of gray- matter is towards inside and that of white -matter is towards outside. In adults, this arrangement continues in the spinal-cord but during the development of the wall of the brain the gray- matter is transferred outside.
31. In 1 minute 750 ml of blood is conducted to the human- brain.
32. Corpus callosum is the largest commissure of the brain.
33. Largest cranial venous sinus is cavernous venous sinus which is situated in the middle cranial fossa.
34. All pre ganglionic sympathetic nerve fibres are myelinated while post ganglionic nerve fibre are non myelinated.
35. In PNS myelinogenesis process is occured by neurilemma (Schwan cells) while in CNS myelinogenesis process is occured by oligodendrocytes (Neuroglia)
36. Alzheimer's disease – In this disease, the cerebral cortex is atrophied and ultimately the ventricle enlarges.
    • Symptoms consist loss of memory particularly recent memory. Alzheimer disease is more common in down syndrome.
    • Treatment – No effective treatment.
37. Stroke – May be caused by haemorrhage into the brain.
    • Symptoms – Unconsiousness.
    • Treatment– Intravenous tissue plasminogen activator.
38. Epilepsy – Epilepsy is characterized by short, recurrent periodic attack of motor, sensory or psychological malfunction.
    • Cause – due to abnormal discharge of cerebral neurons.
    • Symptons – seizures, unconsiousness, Involuntary contraction of muscle.
    • Treatment – Anti epileptic drugs.
39. In human brain more than 100 billion neurons are present.
40. Each neuron cell connect with 25,000 other cell.
41. Phrenic nerve is branch of cervical plexues which supply diaphragm.
42. Malathione :- This substance is used as insecticide and it destroy the acetyl cholinesterase in synapse area.
43. Botulism :- It is food poisoning disease and it produces by Clostridium botulinum bacteria. This bacteria release neurotoxin.
44. Curare : - is drug which blocks acetylcholine receptor on skeletal muscle, so that it can be used by a surgeon for keeping a muscle relaxed during operation.
45. Corpus striatum regutales planning and execution of stereotyped movement.
46. The region between the thalamus and spinal cord is referred to as brain stem.
47. All impulse traversing a given neuron have the same amplitude, differing only in the frequency of impulse.
48. Glycine is neuro inhibitory hormone present in spinal cord.
49. Glutamate is excitatory amino acid.
50. Trigeminal nerve is also called "the dentists nerve" because the dentists desensitizes this nerve with some anaesthetic before pulling out the troubling tooth.
51. Important Nuclei organglia related with cranial nerve

dinger westpal Nucleus →  Oculomotor nerve

Gasserian ganglion→  trigeminal nerve semilumar ganglion

Nervus intermedium →Facial nerve geniculate ganglion