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Home , Epidural space

Central Nervous System - & Cranial Nerves

Chapter 14 Part A Central Nervous System

Central nervous system (CNS) is responsible for: Receiving impulses from receptors Integrating information Sending impulses to the effectors Central Nervous System

Central nervous system (CNS) is responsible for: Receiving impulses from receptors Integrating information Sending impulses to the effectors

It is composed of: Brain Brain

Brain

Cranium

Foramen magnum Spinal cord

Brain is one of the largest organs of the body. Located in the cranial cavity….formed by 8 cranial bones. Connected to spinal cord at foramen magnum. Brain

Brain rapidly grows in fetus and then during early childhood years. Growth of the brain: Neurons stop dividing in an infant. Brain continues to grow due to increase in: Size of the neurons. Number of glial cells. Myelination. Branching of dendrites and axons. Number and size of synapses. Brain - Functions

Brain has the following functions: 1. Receives sensations: receives impulses from all over the body to make it aware of the environment. 2. Integrates information: makes decisions on major functions of the body. 3. Control Center: for temperature, movement, balance, cardiac/respiratory systems, hormones, hunger, thirst, emotions, intelligence, memory, dreaming, learning. Brain - Protection

Brain is protected by bones and 3 connective tissue membranes called . From outside  inside: 1. Boney protection: cranial bones  form cranial cavity  houses brain. 2. : outermost tougher meninx  splits into 2 layers: Outer dura mater – periosteal layer: stick to the periosteum of the cranial bones. Inner dura mater – meningeal layer: wraps around the brain and its crevices. 3. : middle avascular meninx. 4. : innermost meninx that sticks to the brain. Brain - Protection

There are spaces between the protective layers:- 1) Outer periosteal layer is fused to the periosteum of cranial bone- no epidural space.

2) - located in the space between periosteal and meningeal layer-contains veins that carry deoxygenated blood from brain to heart (via internal jugular vein).

3) - potential space between dura mater & arachnoid (space appears when there is trauma or underlying pathological conditions).

4) Subarachnoid space- space between arachnoid and pia mater-contains CSF and network of blood vessels. Brain - Ventricles

Lateral ventricles Interventricular foramen Third ventricle

Cerebral aqueduct

Fourth ventricle

Central canal

Brain is not a solid structure…..it has fluid-filled cavities inside. Ventricles: cavities in the brain…filled with (CSF). Continuous with the central canal of the spinal cord. Lined with ciliated ependymal cells  help form and circulate CSF in the brain and spinal cord. Two lateral ventricles  through interventricular foramina  into third ventricle  through cerebral aqueduct  into the fourth ventricle  through median aperture  into central canal of the spinal cord. Fourth ventricle  through 2 lateral apertures  into subarachnoid space around brain and spinal cord. Cerebrospinal Fluid - CSF

Cranium Dura mater (Outer)

Arachnoid Dural sinus villi CSF reabsorption

Dura mater (Inner)

Subdural space Brain Arachnoid mater

Pia mater Subarachnoid space

Outer, Inner Dura Mater

Cerebrospinal fluid (CSF): It is filtered blood. It circulates in: Central canal of the spinal cord, Ventricles of the brain, Subarachnoid spaces around the brain and spinal cord. From subarachnoid space-via arachnoid villi-CSF drains into dural sinus and gets reabsorbed into blood. Any interruption in the normal circulation/reabsorption of CSF-over accumulation of CSF- e.g. hydrocephalus in infants (abnormal widening of ventricles-enormously expanded ). Cerebrospinal Fluid - Functions

Functions of CSF: Mechanical – cushions, floats and protects the brain inside the cranial cavity. Chemical – maintains ion concentration and pH. Circulates to provide nutrient and pick up waste products. Cerebrospinal Fluid - Functions

Formation of CSF: Formed by . Choroid plexus: Tissue present in the wall of the ventricles. Composed of blood capillaries covered by ependymal glial cells. Forms the Blood-CSF Barrier…..filters blood  forms CSF  protects brain from chemicals/infections blood may carry. Cerebrospinal Fluid - Functions Choroid plexus of lateral ventricle

Blood-CSF Barrier: Choroid plexus – a combination of blood capillaries and ependymal cells. Screens blood: Allows rapid passage of glucose, O2, CO2, water, lipid soluble substances (alcohol, caffeine, nicotine, heroin, anesthetics). Slow passage of urea and ions. Do not allow proteins and most antibiotics to pass.