Nervous System Functions and Divisions

Nervous System Divisions

• The central nervous system (CNS) comprises the brain and spinal cord
• The peripheral nervous system (PNS) consists of cranial nerves, spinal nerves, and ganglia outside the CNS

CNS Function

• The CNS integrates sensory information and issues commands
• Occupies the dorsal body cavity acting as the NS integrating and command center

Functions of the Nervous System

• Maintains body homeostasis through electrical signals and coordinates with the endocrine system to release hormones
• Controls motor, sensory, autonomic, cognitive, and behavioral activities
• Provides sensation, mental functioning, and emotional response
• Activates muscles and glands
• Ten million sensory neurons transmit information about the internal and external environment toward the brain
• Five hundred thousand motor neurons control muscles and glands
• The brain contains over 20 billion nerve cells linking sensory to motor responses
• Neurons that are destroyed cannot be repaired
• The basic functional unit of the brain is the neuron or nerve cell
• Neurons respond to stimuli and are specialized to transmit messages as nerve impulses, and are composed of the bodies

Neurons

• Sensory neurons relay sensory impulses from sensory organs toward the CNS
• Motor neurons carry motor impulses from the CNS to specific effectors

Neuron Structure

• Neurons contain rough endoplasmic reticulum, free ribosomes, a Golgi apparatus, a nucleus, mitochondria, and mictorubules
• Neurons contain hundreds of branching dendrites, with only one axon arising from the axon hillock

Neuron Components

• The cell body (soma) provides life support and holds the nucleus and metabolic center
• Dendrites carry impulses toward the cell body and contains the synapses for receiving electrochemical messages
• Axons conduct impulses away from the cell body

Nerve Cell Support

• Clusters of nerve cell bodies are called neuroglia, or glial cells
• Glial cells support, protect, and nourish neurons
• Clusters of cell bodies with the same function is called a center, like the respiratory center

Neuroglia Types

• Astrocytes support and regulate ions in the CNS
• Satellite cells surround neuron cell bodies in the PNS
• Microglial cells defend the CNS through phagocytosis
• Schwann cells insulate PNS neuron cell bodies, and help form myelin sheaths
• Ependymal cells line cavities where CSF moves

Axons and Impulses

• Axonal terminals are separated by synaptic clefts, which are gaps between adjacent neurons
• Synapses are junctions between nerves
• Axonal terminals contain neurotransmitters

Neurotransmitters

• Neurotransmitters are chemical messengers between neurons or from neurons to target tissue
• Neurotransmitters communication happens from one neuron to another or from a neuron to a specific target tissue
• A neurotransmitter has an affinity for receptors in the postsynaptic bulb
• Transmitters have an affinity for specific receptors in the postsynaptic bulb

Neurotransmitter List

• Acetylcholine, found in many areas of the brain and the autonomic nervous system, is usually excitatory but with parasympathetic effects, can restrain heart stimulation via the vagal nerve
• Serotonin, found in the brain stem, hypothalamus, and dorsal horn of the spinal cord, help control mood and sleep, inhibits pain pathways
• Dopamine, found in the substantia nigra and basal ganglia, restrains, and affects behavior like attention, emotions & fine movement
• Norepinephrine, stemming from the brain stem & hypothalamus, is usually excitatory and affects mood/overall activity
• Gamma-aminobutyric acid (GABA), concentrated in the spinal cord, cerebellum, basal ganglia and some cortical areas, is an excitatory Amino Acid
• Enkephalins & endorphins, release from nerve terminals in the spine, brain stem, thalamus, hypothalamus, and pituitary gland, are excitatory, create pleasurable sensation, and inhibit pain transmission

Structures within the brain

• The hippocampus aids in learning
• The ventral tegmental area, lies in the midbrain, and can control diverse behaviors

Central Nervous System Regions

• The CNS contains four major regions being the cerebrum, brain stem, cerebellum, and diencephalon
• The average adult human brain weighs 1.3 to 1.4 kg, about 2% of total body weight.
• Brain tissue is pinkish gray, wrinkled, and has the texture of cold oatmeal

Cerebrum

• The largest part of the brain comprising over half of its mass
• The cerebrum consists of two hemispheres incompletely separated via the longitudinal fissure.
• The corpus callosum sends data from one hemisphere to the other
• Transferred data includes sensation, memory, and learned discrimination

Cerebral Hemispheres

• The outer surface of the hemispheres are wrinkled because of the amount of gyri or folds on tissue
• Gyri increases the surface area of the brain
• Gray matter is the outer section or exterior part that is composed of billions of neurons, thus the gray appearance
• White matter is the inner level, and holds nerve fibres and neuroglia/support tissue

Cerebral Lobes

• Parts include the Frontal, Parietal, Occipital, and Temporal Lobes

Frontal Lobe

• The largest lobe, in charge of - Concentration, abstract thought, data storage or storage, motor movement
• Broca's area, contained within, is needed for for motor control of speaking
• Responsible for persona, judgement, and suppressing

Parietal Lobe

• The somatic sensory area position posterior to the Central Sulcus
• Primary sensory cortex analyzes and give sensory data
• Necessary for awareness of the body as it exists in area, and has orientation in space

Occipital Lobe

• Consists of visual area
• In control of visual evaluation and translation

Temporal Lobe

• The auditory location
• Contains a key area known as Interpretive Area
• Integrates somatization, visual, and auditory data
• Highly dominates in cerebration the brains action by thinking

Cerebral Areas

• Specialized areas control taste (gustatory), sight (vision), hearing, and scent (olfactory)

Sensory Pathways

• Operate by crossed pathways that cause the left cortex gets reactions from right side of body,and vice-versa

Hemispheres

• Right cerebral hemisphere is holistic, conceptual, and synthesizing-NON-VERBAL
• Left cerebral location is analytic, technical - VERBAL
• Right limb controls interpersonal, emotional, and symbolic expression
• Left lobe controls planning, and admin
• The right brain is spatial and holistic while the left is analytical.

Other Brain Info

• Corpus Callosum transfers Right and left Data through the brain
• Right-handed, as well as few left-handed humans are analytical and language is dominant
• Non-dominant regions of the brain are in charge of spatial, visual and artistic functions

Basal Ganglia

• Holds masses, position deeply within the hemispheres
• Fine motor movements rely on that, including of hands, as ell as lowers
• Involved in Coordination of movement

Thalamus Info

• Primarily acts to relay feeling and sensation with the exception of smell
• Data of pain, Memory, etc, all must go through that part, both negative as well as pleasant

Hypothalamus Data

• Lies Anterior, and inferior to the Thalamus
• The infundibulum (hypothalamus) link it to rear pituitary gland
• Heavily needed for action and activity of pituitary gland, influence all areas
• In control of internal water and temperatures

Other notes

• Can use certain drug types to act to promote regulation by increasing certain actions
• Mammillary areas can help reflex via the nose, bulge via hypothalamus and rear pituitary gland
• Limbic region effects emotional expression to action or physical action

Brain Details

• Pituitary gland is below Diencephalon, to be exact
• Sits within structure
• Tumors typically arise
• Hormone imbalance will be seen

Important Notes

• Rear of hemisphere focus on actions, for each
• Side is for the ears as the middle if for touch
• The front actions promote feeling

Brain Stem Components

• Parts entail Midbrain,Pons and Medulla
• Both feelings and actions need it to operate normally
• Cranial nerve pairs 3,4 have their roots in mid brain

Pons Details

• Rests in the front of the cerebellum through midbrain and also Medulla, bridging through 2 sides of it
• Holds sets of 5,6 ad also the two 7. 8 parts
• Motor actions are seen

Medulla oblongata

• Holding physical aspects of the spinal
• Cranial are needed as well
• All function needs those pieces

Cerebellum Details

• Set off from sides, having much action
• fine actions take place needing it,

Brain Protection

• Has 3 connective pieces
• First, the the skin, then bone, then membranes

CSF information

• moves about in areas inside/outside surface
• flow is important, flow begins by the foremen monroe, then over to thirds and sylvius

Layers of Meninges

• The Dura known as the outer
• Arachnoid the area in middle
• then lastly the pia which is innnermost

Dura Mater

• outer most area, that wraps CNS
• gray, and lacks the in or elasticity
• The cerebrum can break though it
• Falx Cerebelli in the rear of bottom cortex region

Arachnoid layer

• area that has the middlemost
• with not much inner supply
• holds vessels and projections
• the subdural can hold fluid volume

Pia Mater

• inner lining which connects to CNS
• A transparent sheath that holds to external surface

CSF Information

• very clear liquid needed that runs in surface
• CSF fluid can exist every area

Blood Supply Details

• CNS must always hold that flow
• with brain arteries reaching those smaller points

Circle of Willis

• has many parts to act to provide brain its needed flow
• and assist to circulate many actions and fluids

Veins

• Brain flow is assisted with blood and gravity

Spinal Cord Details

• acts for body's motions, or also response