Nervous System

• The nervous system communicates and maintains homeostasis
• Neurons and nerves facilitate communication within the nervous system

Divisions and Functions

• The central nervous system (CNS) contains the brain and spinal cord, serving as the central processing center
• The peripheral nervous system (PNS) is a network of nerves throughout the body that sends messages to and from the CNS

CNS Subdivisions

• The cerebrum is divided into lobes
• Diencephalon consists of the hypothalamus and thalamus
• The brainstem includes the medulla oblongata, pons, midbrain, and reticular formation
• Cerebellum is also part of the CNS

PNS Compositions

• Sensory neurons carry afferent (incoming) messages to the brain or spinal cord
• Motor neurons carry efferent (outgoing) messages away from the brain and spinal cord

Autonomic and Somatomotor Divisions

• Somatomotor division controls skeletal muscles for body movement
• The autonomic division sends efferent messages to glands, cardiac muscle, and smooth muscle of hollow organs and blood vessels

Autonomic Subdivisions

• The parasympathetic division is for vegetative activities like digestion
• The sympathetic division prepares the body for physical activity, known as fight or flight

Neuron Anatomy

• Neurons have dendrites that receive information, a body containing the nucleus, and an axon that carries nerve impulses

Neuron Components

• Dendrites: Neurons have 1 to 1,000 dendrites for information processing
• Body: Contains the nucleus and produces neurotransmitters
• Axon: Carries electrical messages to the terminal arborization

Clinical Consideration:

• An imbalance of specific neurotransmitters leads to disorders like depression

Axonal Transport

• Neurotransmitters are transported down the axon for release

Retrograde Axonal Transport

• Empty synaptic vesicles are carried back to the body for reuse

Axon Details

• Axons leave the cell body at the axon hillock/trigger zone
• Messages travel down to the terminal arborization
• Synaptic knobs at the end of branches form a synapse with another cell

Myelin Sheath

• Axons are intermittently covered with myelin
• Myelin is lipid-rich and insulates axons, with gaps called Nodes of Ranvier

Matter Colors

• White matter has myelinated axons
• Gray matter contains dendrites, cell bodies, and unmyelinated axons
• Peripheral nerves have myelinated axons

Neuron types

• Multipolar neurons (most common) have multiple dendrites and an axon
• Bipolar neurons have one dendrite and one axon, found in the nasal cavity, retina, and inner ear

Unipolar Neurons

• Unipolar neurons have one process serving as both dendrite and axon
• These are sensory neurons located areas like skin and organs
• Cell bodies of unipolar neurons form ganglia

Neuroglia Overview

• Neuroglia are support cells outnumbering neurons

Neuroglia

• Oligodendrocytes: form myelin in the CNS and can myelinate more than one axon
• Ependymal: neuroglia line fluid-filled cavities, produce cerebrospinal fluid (CSF)

Astrocytes

• Astrocytes: most numerous neuroglia in the CNS, covering nonmyelin portions of neurons and blood vessels
• Creating a blood-brain barrier, also regulate CSF content, and fill damaged areas with scar tissue

Microglia

• These act as macrophages to remove damage, debris, and pathogens

PNS Neuroglia

• Schwann cells: form myelin in the PNS and help regenerate damaged axons
• Satellite cells: control the environment for ganglia in the PNS

Meninges Overview

• Meninges cover the brain and spinal cord and consist of three membranes

Meninges Structure

• Dura mater is the tough, superficial layer
• Arachnoid mater is a delicate, weblike layer
• Pia mater is tight to the brain and spinal cord

Cavities Overview

• The epidural space, between vertebrae and dura mater, contains blood vessels and adipose tissue
• The subarachnoid space, between arachnoid and pia mater, contains cerebrospinal fluid

CSF info

• Ependymal cells lining brain ventricles make CSF
• Choroid plexus is a bed of capillaries in ventricle walls
• Around 500 mL of CSF produces daily and roughly 100 to 160 mL are preasent at a time

CSF func:

• CSF provides buoyancy, protection, chemical stability, and nutrients

Brain organization

• The brain has four subdivisions: cerebrum, diencephalon, brainstem, and cerebellum

Cerebrum

• Cerebrum is characterized by gyri (folds) and sulci (grooves)
• It is divided into right and left hemispheres

Hemispheres

• Longitudinal fissure separates hemispheres
• The corpus callosum connects them
• Cortex (superficial part) has gray matter, responsible for conscious thought

Lobe Breakdown

• Five major lobes includes the named for underlying cranial bones + insula
• Each contains a sensory area for sensory message analysis

Thalamus

• The thalamus is a switching station for incoming sensory messages

Hypothalamus

• Regulation of temperature, Autonomic functions like heart rate, Endocrine functions involving hormone production, Food and water intake (hunger, thirst), and Sexual development

Brainstem Subdivisions

• Medulla, pons, midbrain, and reticular formation

Medulla Oblongata

• Ascending sensory messages pass through the medulla oblongata to thalamus
• Descending motor messages passes through medulla oblongata before reaching the spinal cord

Efferent Motor Messages

Motor messages cross sides at the pyramids, so messages from right control the left

• Regulates Heart rate/respiratory rate/diameter and more

Pons Function

Sensory messages runs to the thalamus & motor tracts from cerebrum goes through here

• Serves as a bridge for cerebellum motor messages

Midbrain Function

• Has 4 bulges called colliculi for visual and auditory reflexes

Reticular Formation

• Determines the cerebrum receives awareness of Sensory messages
• Also, responsible for the sleep-wake cycle

Cerebellum

• The cerebellum receives position information and motor information
• Uses information to maintain coordination and balance

Spinal cord function

• The spinal cord starts at the foramen magnum to L1 of vert cavity
• The solid with nerve root called cauda equina

Spinal Cord Size

• Enlarged in cervical and lumbar
• Total 31 pairs of spinal nerves that connect to the spinal cord

Spinal Cord Structure

• Has an “H” shape + made of dendrites and more
• Axons in ascending sends message to the white
• Axons can also descend messages too

Peripheral Nerve Anatomy

• Nerves are like nerves that fibers similar
• Endoneurium surrounds axon
• Fascicles are bundles that surrounds perineurium
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Nerve Types

• Sensory that runs all afferent axons, some efferent motors
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Spinal Nerve Divisions

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