Diencephalon{hap ii}

THALAMUS ,HYPOTHALAMUS,EPITHALAMUS----STRUCTURE & FUNCTIONS ; SPNAL CORD ,REFLEX ACTION ETC.......

1. BRAIN & SPINAL CORD Presented by: HEENA PARVEEN M.Pharm . Dept. of Pharmacology, Asst.Professor , DNVP.

2. Diencephalon Forms central part of forebrain. It is enclosed by cerebral hemispheres & includes 3 paired structures namely THALAMUS,HYPOTHALAMUS,EPITHALAMUS.

3. Thalamus It is a paired, ovoid, large mass of grey matter, with length of 3cm. Lcn : on lateral walls of 3 rd ventricle. 80% of diencephalon is Thalamus. Both thalami of right & left halves are connected by grey matter & separeted by whole matter with a septum Y-shaped-----Internal medullary laminna .

4. Functions: It acts as a relay centre for receiving sensory impulses from spinal cord & brain stem to primary sensory areas of cerebral cortex. They play role in arousal & alertness. It also acts a centre for motor functions, where it transmits impulses form cerebellum & basalganglia to primary motor area of cerebral cortex. It serves to control emotional & behavioural aspects.

5. Hypothalamus It is a small part of Diencephalon, below the thalamus & above PG. It contains about 12 nuclei in 4 main regions. They are as Mamillary region Tuberal region Supraoptic region Preoptic region Fncns : Hormone production Thermoregulation Emotional & Behavioural control Eating & Drinking control Controlof circardian rhythm.

6. Epithalamus It is the most dorsal portion of Diencephalon. T includes pine cone shaped pineal glad & habenular nuclei. Pineal gland secretes hormone Melatonin, therefore it is considered as a part of endocrine system. Melatonin secreted during darkness, helps in controlling circardian rhythm.

7. SPINAL CORD External Anatomy: Roughly oval shape, Elongated, cylindrical, begins from M.O & extends until the 2 nd lumbar vertebrae. In adult males—S.C reaches a length of 45cm, In females– shorter about 43cm.The diameter varies all along the length 2cm greatest in middle & smallest towards tip.

8. Internal Anatomy: T s composed of Grey matter & White matter.In contrast to brain, grey matter is found at central regions & white matter at the periphery .

9. Grey matter: It is arranged as H /Butterfly Composition: Neuronal cell bodies, Dendrites, Unmyelinated axons, Glial cells. Grey commisure –Cross bar of H,houses a small cavity know as Central canal that contains CSF. Subdivisions: Posterior Grey Horn; Anterior Grey Horn; Lateral Grey Horns. White matter: It is arranged peripherally & divided in to left & right sides by 2 grooves : Namely—Posterior median sulcus on posterior side & anterior median fisure on anterior side.. Left & right sides are connected by ‘ Anterior white commissure ’. White mater consists of myelinated axons. Subdivisions: Anterior white column/Ventral W.C Posterior White column/ Dorsal W.C Latreal white column.

10. Physiology of SPINAL CORD It functions to maintain homeostasis.oth sensory ascending tracts & motor descending tracts run through the spinal cord help in conducting the impulses to & from the brain. ASCENDING TRACTS : To convey sensory information from receptors to brain .2 tracts are— Spinothalamic tract—Originates in S.C & terminates In thalamus. Mainly concerned with the impulse transmission of pan, coolness, warmth, Tickle,deep pressure. Posterior column– a) Gracile fasciculus:relay information from lower thoracic,sacral,coccygeal segments to nucleus gracilis in M.O. b) Cuneate fasciculus: to transmit impulses from cervical to nucleus cuneatus M.O.

11. DESCENDING TRACTS: Have motor function. Information received through the ascending sensory tracts is processed in the CNS & motor responses are transferred to effector organs via descending tracts. DIRECT TRACTS: Lateral cortico -spinal tract-brings about the voluntary movements of distal ends . Anterior cortico -spinal tract- concerned with movements of the trunk & proximal portions of limbs. Cortico -bulbar tract- in movement of head & neck. 2. INDIRECT TRACTS: Rubrospinal tract-in voluntary movements of upper parts. Tecto spinaltract - In reflex movements of eyes ,head, trunk. Vestiulo -spinal tact- maintains posture & balance . Reticulo-spial tract- Maintainence of posture & modulating muscle tone .

12. REFLEX ACTION Reflexes– It is defined as rapid ,automatic ,predictable & involuntary responses to a particluar stimuli. Ex: Removal of hand after touching the hot object is Reflex.

13. Somatic reflexes –In +N of voluntary skeletal muscles.Ex : Knee jerk on tapping tendons. Autonomic reflexes– In contraction of involuntary structures lyk Cardiac muscles, smooth muscles, & glands. Ex: Constriction of eye pupil on torch light. Spinal reflexes– Sensory input is integrated in the spinal cord. Cranial reflexes—Brain is the integration centre. Unconditioned reflexes– Inborn reflexes which cannot be changed normally. Ex: Hand withdrawl on touching hot objects.

14. REFLEX ARC

15. Neural pathway involved in production of reflex is known as Reflex arc/Reflex circuit. 5 basic components of REFLEX ARC are: Sensory receptor —This R in response to stimuli produces a Graded potential which on reaching threshold value ,generates nerve impulse. Sensory neuron– Impulse propagates through axon reaches integration region (grey matter) . Therefore ,these functions to transmit sensory input from periphery to cns . Integration centre– Maybe Brain /S.C. Input integrated & motor response elicited. Motor neuron– Motor response from integration centre is transmitted to the effectors via motor neurons. Effector – Action produced by the effector is termed as Reflex .