Nervous System Functions

• The nervous system is the body's primary control and communication network

Functions of the Nervous System

• Sensory receptors monitor internal and external changes
• Sensory input is processed and interpreted
• Integration involves decision-making based on the input
• Motor output activates muscles or glands (effectors) to produce a response

Homeostasis Regulation

• The nervous system uses fast-acting electrical impulses for control
• The endocrine system uses slower-acting hormones released into the blood

Central Nervous System (CNS)

• The CNS includes the brain and spinal cord
• It integrates sensory information and serves as a command center
• Instructions are issued based on experience and current conditions

Peripheral Nervous System (PNS)

• The PNS consists of cranial and spinal nerves
• It functions as a communication line, linking all body parts

Nerves

• Cranial nerves carry impulses to/from the brain
• Spinal nerves carry impulses to/from the spinal cord

Ganglia

• Ganglia are clusters of nerve cell bodies

Sensory Neurons

• Sensory (afferent) neurons carry impulses to the CNS

Types of Sensory Fibers

• Somatic sensory fibers transmit impulses from skin, muscles, and joints
• Visceral sensory fibers transmit impulses from visceral organs

Motor Neurons

• Motor (efferent) neurons carry impulses from the CNS

Somatic Nervous System

• The somatic nervous system allows conscious control of skeletal muscles

Autonomic Nervous System (ANS)

• The autonomic nervous system regulates involuntary activities like cardiac muscle, smooth muscle, and glands

ANS Divisions

• The sympathetic division triggers the "fight or flight" response
• The parasympathetic division promotes "resting and digesting" and conserves energy

Neuroglia

• Neuroglia support, insulate, and protect neurons
• They do not conduct impulses or undergo cell division

Neurons

• Neurons are nerve cells that transmit impulses and are the functional unit of the nervous system

Interneurons

• Interneurons connect sensory and motor neurons

Glial Cells

• Glial cells offer support, insulation, and protection to neurons

CNS Neuroglia

• Astrocytes, oligodendrocytes, microglia, and ependymal cells

PNS Neuroglia

• Schwann cells and satellite cells

Astrocytes

• Support/anchor neurons to capillaries
• Protect from harmful substances in blood and maintain the blood-brain barrier
• Control the chemical environment, remove excess ions, and recapture neurotransmitters
• Regulate neural communication

Microglia

• Provide immune response in the CNS
• Dispose of debris like dead cells and bacteria

Ependymal Cells

• Secrete and circulate cerebrospinal fluid, forming a protective cushion

Oligodendrocytes

• Insulate neurons in the CNS with myelin
• Form white matter in the brain
• Increase the speed of nerve transmission

Schwann Cells

• Provide myelin insulation to neurons in the PNS by wrapping around the axon

Satellite Cells

• Support, anchor, protect, and cushion neurons in the PNS

Neuron Anatomy

• The cell body houses organelles and receives impulses from dendrites
• The axon sends impulses away from the cell body
• Dendrites bring impulses towards the cell body
• Axon terminals release neurotransmitters
• Collateral branches extend off the axon
• The synaptic cleft (synapse) separates the axon terminal from the next neuron's dendrite
• The neurolemma is the outermost part of a Schwann cell and aids in neuron regeneration
• Nodes of Ranvier are gaps in the myelin sheath

White and Grey Matter

• White matter consists of dense bundles of myelinated fibers
• Myelin insulates axons to increase impulse speed
• Gray matter consists of unmyelinated fibers and cell bodies

Neuron Types

• Unipolar neurons have a short, single process that divides into peripheral/distal and central/proximal processes, describing sensory neurons in the PNS
• Bipolar neurons have two processes from the cell body
• Multipolar neurons have many processes and are the most common type; all motor & interneurons are multipolar

Nerve Impulse Pathway

• Impulse travels: dendrite -> cell body -> axon -> terminal branches -> synapse

Unipolar Neuron Processes

• The peripheral/distal process contains dendrites
• The central/proximal process contains axon terminals

Reflex Arc

• The reflex arc is a direct connection between sensory and motor neurons, allowing rapid response to stimulus without conscious involvement

Reflexes

• Reflexes are rapid, predictable, involuntary responses to stimuli

Reflex Types

• Somatic reflexes stimulate skeletal muscles (e.g., pulling a hand away from a stove)
• Autonomic reflexes regulate smooth muscles, the heart, and glands (e.g., salivation, pupil size changes)

Brain Regions

• The main parts of the brain include the forebrain, midbrain, and hindbrain

Brain: Forebrain

• The forebrain contains the cerebrum and hypothalamus

Brain: Midbrain

• The midbrain relays information to the cerebrum and controls body movement and posture

Nerves

• A nerve is a bundle of neuron fibers held together by connective tissue

Nerve Layers

• Endoneurium surrounds individual nerve fibers
• Perineurium binds groups of fibers into fascicles
• Epineurium binds fascicles together

Fascicles

• Fascicles are groups of muscle fibers

Cerebrospinal Fluid (CSF)

• Cerebrospinal fluid protects the brain by preventing impact with the skull and is produced by the 4 ventricles

Choroid Plexus

• The choroid plexus consists of capillaries that secrete CSF and hang from the roof of each ventricle

Meninges

• Meninges are 3 continuous connective tissue layers that protect the spinal cord and brain

Meninges: Dura Mater

• The dura mater is the tough, outer layer

Meninges: Arachnoid Membrane

• The arachnoid membrane is the thin, cobweb-like middle layer

Meninges: Pia Mater

• The pia mater is the thin, inner layer containing blood vessels and attaches to the surface of spinal cord and brain

Integration

• Integration is the processing and interpretation of sensory input

Cerebrum

• The cerebrum is the largest part of the brain, divided into left and right hemispheres

Corpus Callosum

• The corpus callosum is a broad band of nerve fibers connecting the two brain hemispheres

Cerebral Cortex

• The cerebral cortex is the outer layer of the cerebrum composed of interconnected neural cells; it is the control and information-processing center and consists of gray matter

Brain Surface Features

• Gyrus (gyri) denotes elevated ridges on the cerebral cortex
• Sulcus (sulci) denotes shallow grooves
• Fissures are deep sulci that separate large brain areas

Frontal Lobe

• Involved in planning, judgment, speaking, voluntary muscle movement, reasoning, impulse control, memory, and predicting consequences

Primary Motor Area

• Initiates voluntary skeletal muscle movement

Premotor Area

• Processes input on body movement and modifies movements

Broca's Area

• Controls facial muscle movements for speech production (language expression), located in the Frontal Lobe

Wernicke's Area

• Is involved in language comprehension and meaningful expression, and is located in the temporal lobe

Somatic Sensory Area

• Registers and processes touch and movement sensations

Parietal Lobe

• Receives sensory input for touch, pain, temperature, and body position (spatial abilities)

Temporal Lobe

• Involved in auditory processing, smell, and recognizing faces, words, and names

Occipital Lobe

• Processes visual input and object memory

Diencephalon

• Contains the thalamus, hypothalamus, epithalamus, and pineal gland within the cerebrum

Thalamus

• Filters and relays sensory information (except smell) to cerebral cortex, cerebellum, and medulla

Hypothalamus

• Directs maintenance activities (eating, drinking, body temperature)
• Governs the endocrine system via the pituitary gland
• Is part of the limbic system, regulating emotions and feelings of pleasure
• Controls the autonomic nervous system for automatic functions

Epithalamus

• Contains the pineal gland

Pineal Gland

• Secretes melatonin to regulate daily body rhythms

Brain Stem

• Manages automatic survival functions (heartbeat, breathing)
• Sends/receives information

Brain Stem Parts

• Midbrain, pons, medulla oblongata, and reticular formation

Pons

• Carries information between brain sides
• Centrally controls breathing

Reticular Formation

• Involved in arousal, filtering signals to thalamus, sleep, and attentiveness

Substantia Nigra

• Helps smooth body movements; damage leads to Parkinson's disease

Ventral Tegmental Area (VTA)

• Midbrain area producing dopamine; associated with mood, reward, and addiction

Medulla Oblongata

• Transmits impulses between the spinal cord and brain; controls blood pressure, heart rate, swallowing, and coughing

Cerebellum

• Concerned with balance and smooth coordination
• Processes sensory input
• Supports nonverbal learning and memory

Amygdala

• Linked to emotion
• Sends signals activating fight or flight
• Explains the effect smell has on memory

Hippocampus

• Involved in explicit memory formation of facts and events and learning

Spinal Cord Horns

• Dorsal horns receive impulses from sensory neurons
• Ventral horns receive impulses from motor neurons

Cranial Nerves

• Cranial nerve I: Olfactory (sensory)

The nervous system is the body's primary control and communication network. It consists of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS includes the brain and spinal cord, while the PNS consists of cranial and spinal nerves.