Central Nervous System - Brain & 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 Spinal cord
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 meninges. From outside inside: 1. Boney protection: cranial bones form cranial cavity houses brain. 2. Dura mater: 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. Arachnoid mater: middle avascular meninx. 4. Pia mater: 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) Dural venous sinuses- located in the space between periosteal and meningeal layer-contains veins that carry deoxygenated blood from brain to heart (via internal jugular vein). 3) Subdural space- 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 cerebrospinal fluid (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 Arachnoid villi Cranium Dura mater (Outer) Dural sinus CSF reabsorption Dura mater (Inner) Brain Subdural space 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 skulls).
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. 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.