14.1b Central Nervous System - Brain Stem & Spinal Cord

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General Training Module CENTRAL NERVOUS SYSTEM RK 2

Unit 10 – Nervous System:

Unit 10 – Nervous System Part A – Central Nervous System Part B – Peripheral Nervous System Part C – Autonomic Nervous System Part D – Sensory Organs & Systems

The Nervous System – Contents :

The Nervous System – Contents Overview of the Nervous System & its components The Central Nervous System The Brain and its parts The Spinal Cord an its parts The Meninges of the CNS The ventricles of the Brain, The Spinal Canal & Cerebro - Spinal Fluid (CSF)

Brain Stem:

Brain Stem Mid brain Pons Medulla Oblongata

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Brain Stem

Mid Brain:

Mid Brain This is the part of the brain stem between the cerebrum above and the pons below It consists of nerve cells and fibers that connects the cerebrum above with the deeper parts of the brain and the spinal cord Nerve cells acts as relay stations for the ascending and descending nerve fibers (Tracts)

Pons:

Pons Situated in front of the cerebellum between midbrain and medulla oblongata. It mainly consists of: Nerve fibers: Which form a bridge between the two hemispheres of the cerebellum and the Fibers passing from the higher levels of the brain and the spinal cord ( ascending and descending tracts ) Groups of Cells: That act as relay stations Those that are associated with cranial nerves The cells lie deep while the fibers are superficial

Medulla Oblongata:

Medulla Oblongata This is about 2.5 cm in length an extends from the pons above to the spinal cord below. Lies within the cranium immediately superior to foramen magnum . Has a fissure in the midline both anteriorly and posteriorly The fibers lie peripherally while the nerve cell bodies lie deep.

Medulla Oblongata:

Medulla Oblongata Fibers constitute those that pass between the spinal cord and the higher levels of the brain Cells constitute those that act as relay stations for sensory nerves passing from the spinal cord to the cerebrum Medulla also has vital centers that control autonomic reflexes lie in its deeper structure: Cardiac Center Respiratory Center Vasomotor Center Centers for swallowing, vomiting, coughing and sneezing.

Medulla Oblongata:

Medulla Oblongata Majority of motor and sensory fibers that run through the medulla cross over from left side to right side and vice versa. They are known as: Motor Decussation Sensory Decussation This means that left hemisphere of the brain controls the right half of the body and vice versa And sensory inputs from the left side of the brain is perceived in the right cerebral hemisphere and vice versa

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Mid Brain 1 st Part of Brain Stem

Reticular Formation:

Reticular Formation The  reticular formation  is a set of interconnected nuclei that are located throughout the brainstem. The reticular formation is not anatomically well defined because it includes neurons located in diverse parts of the brain. The neurons of the reticular formation all play a crucial role in maintaining behavioral  arousal and consciousness.

Cerebellum:

Cerebellum

Cerebellum:

Cerebellum Lies behind the pons in the mid-brain Posterior and inferior to the cerebral hemispheres in the Posterior Cranial Fossa in the cranium Has two hemispheres separated by a narrow median strip called vermis Grey matter lies near to the surface where as white matter lies deeper

Functions of the Cerebellum:

Functions of the Cerebellum Proprioception is the main function of the cerebellum. That is co-ordination of voluntary muscle movement, posture and balance. The cerebellar activities are carried out below the level of the consciousness – that is they are not under voluntary control. The sensory input to carry out this function comes from the muscles and joints of the body and the eyes and the ears. It modifies the motor output of the cortex and the brain stem The cerebellar output is inhibitory

Spinal Cord:

Spinal Cord

CNS - The Spinal Cord :

CNS - The Spinal Cord It is an elongated, almost cylindrical structure Extends from the medulla oblongata above downwards starting from the upper border of the atlas It lies within the vertebral canal surrounded by vertebrae. It ends at the 1 st Lumbar vertebra level below. About 45 cm in length (average) and about the thickness of the little finger

The Spinal Cord :

The Spinal Cord It carries the fibers of the spinal nerves, both sensory and motor At each level spinal nerves leave the cord to supply the structure in that region or to carry sensory inputs from the structures to the central nervous system. In the middle is the central canal which is a continuation of the fourth ventricle of the brain and it opens to subarachcnoid space at the end of the cord

The Spinal Cord :

The Spinal Cord It is covered by the 3 meninges that are continuous with the meninges of the brain It is bathed in CSF in the sub-arachnoid space You could see the grey matter in the middle surrounded by white matter in a cross section of the spinal cord. (the opposite arrangement to the brain)

The Spinal Cord – Cross Section:

The Spinal Cord – Cross Section

Grey Matter:

Grey Matter In the cross section of the spinal cord Grey Matter is arranged in “H” shape. Anterior horns and posterior horns are continuous with each other on either side and they are connected in the middle by a transverse commissure In the middle of the transverse commissure is the spinal canal.

White Matter:

White Matter White matter contain the nerve fibers and the glial cells of the spinal cord. White matter consists of Ascending or afferent tracts Descending or efferent tracts In addition fibers of the connector neurons – they are responsible in executing spinal reflexes

Ascending Tracts:

Ascending Tracts Ascending tracts sends sensory inputs from the peripheral spinal nerves to the brain Receive sensory inputs from: Cutaneous (SKIN) nerve ends: touch, pressure, heat and cold Proprioceptive information from: muscles, tendons and joints (they are initiated by stretch receptors) The ascending tracts take information to the brain from these sensory organs

Descending Tracts:

Descending Tracts While descending tracts take motor signals from the brain to the motor component of the spinal nerves. They control skeletal (voluntary) muscle contraction.

The Spinal Reflexes :

The Spinal Reflexes Some activities of the cord are independent of the brain – Spinal Reflexes To facilitate this there are extensive neuronal connections between sensory and motor nerves within the cord at the same level or at different near by levels. Spinal Reflexes occurring via connector neurones or inter- neurones Stretch reflexes occurring without an inter- neurone

The Meninges of the CNS:

The Meninges of the CNS The brain and the Spinal cord are covered by three membranes called meninges: Dura Mater – dense fibrous tissue Arachnoid Mater – a delicate serous membrane Pia Mater – fine connective tissue These meninges lie between the bone of the skull and the vertebrae and the brain and spinal cord They perform a protective function for the central nervous system

Meninges:

Meninges

Meninges:

Meninges

Meningeal spaces:

Meningeal spaces Epidural space – between the bone and the dura mater Subdural Space – between the dura mater and the arachnoid mater There is a potential space between the two layer of dura that give rise to venous sinuses of the brain when expanded at specific sites. Sub- arachnoid space – between the arachnoid mater and the pia mater this contains the cerebro -spinal fluid (CSF)

Meninges of the Spine – cross section:

Meninges of the Spine – cross section

Cerebrospinal Fluid (CSF):

Cerebrospinal Fluid (CSF) CSF is a fluid that fills the ventricles inside the brain, central canal of the spinal cord and is continuous with the subarachnoid space outside the whole central nervous system. The CSF is produced in the ventricles of the brain (mainly in the lateral ventricles)

Cerebrospinal Fluid (CSF):

Cerebrospinal Fluid (CSF) CSF that flows down in the ventricular system of the brain is also continuous with the CCSF in the central canal of the spinal cord. This CSF inside the brain and spinal cord flows to the subarchnoid space through foramina in the ventricles and the opening of the central canal of the spinal cord at its termination. The Subarachnoid space therefore is filled with CSF fluid bathing the brain and the spinal cord with this fluid

Functions of CSF:

Functions of CSF It acts as a shock absorber cushioning the brain and the spinal cord inside their bony cages (skull and the vertebral column) Supports and protects the brain and the spine Maintains a uniform pressure around them Keeps them moist and provides nutrient/eliminate waste

Lumbar Puncture:

Lumbar Puncture Self Study question: Find out what a Lumbar Puncture? When is a Lumbar Puncture performed?

End of Unit 10 – Part A2:

End of Unit 10 – Part A2

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