BIO 180 - Human Anatomy and Physiology I Lecture Study Guide

Functions of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord; responsible for processing and integrating information.

• Peripheral Nervous System (PNS): All nerves outside the CNS; divided into sensory (afferent) and motor (efferent) systems.

• Sensory (Afferent): Sends information to the CNS.

• Motor (Efferent): Sends commands from the CNS to effectors (muscles and glands).

• Somatic Nervous System: Controls voluntary movements.

• Autonomic Nervous System: Controls involuntary functions, further divided into:

  • Sympathetic: Prepares the body for stress-related activities (fight or flight).

  • Parasympathetic: Conserves energy and restores the body to resting state (rest and digest).

Parts of a Neuron

• Axon: Long projection that conducts impulses away from the cell body.

• Cell Body (Soma): Contains the nucleus; integrates signals from dendrites.

• Dendrite: Branch-like structures that receive signals from other neurons.

• Axoplasm: Cytoplasm of the axon, provides a medium for transport.

• Axolemma: Membrane enclosing the axon.

• Myelin: Fatty substance that insulates the axon, increasing transmission speed.

• Nodes of Ranvier: Gaps in myelin sheath that facilitate saltatory conduction.

• Schwann Cell: Glial cell that forms myelin sheaths in the PNS.

• Nucleus: Control center of the neuron containing genetic material.

• Terminal Bulb: End of the axon where neurotransmitter release occurs.

• Collaterals: Branches of the axon that allow communication with multiple cells.

• Axon Hillock: Cone-shaped region of the axon where action potentials are generated.

Classifications of Neurons

• Sensory (Afferent) Neurons: Transmit sensory information to CNS.

• Motor (Efferent) Neurons: Carry commands from CNS to muscles.

• Interneurons: Connect sensory and motor neurons; found exclusively in CNS.

• Somatic Motor Neurons: Control voluntary muscles.

• Autonomic Motor Neurons: Control involuntary muscles and glands.

• Anaxonic Neurons: Lack identifiable axons; involved in local communication.

• Bipolar Neurons: One axon and one dendrite; found in sensory organs.

• Multipolar Neurons: One axon and multiple dendrites; most common type.

• Unipolar Neurons: One process that divides into an axon and a dendrite; primarily sensory.

• Pseudounipolar Neurons: Single process that bifurcates into two branches; mainly sensory.

Neuroglial Cells Functions

• Schwann Cells: Form myelin in the PNS.

• Oligodendrocytes: Form myelin in the CNS.

• Microglia: Act as immune defense in the CNS.

• Astrocytes: Maintain the blood-brain barrier and regulate blood flow.

• Ependymal Cells: Line brain ventricles; involved in cerebrospinal fluid production.

• Satellite Cells: Support and protect neuronal cell bodies in the PNS.

Myelination Process and Function

• Myelination enhances the speed of electrical impulse transmission along the axon.

• Formed by glial cells wrapping around the axon; increases conduction efficiency through insulation.

• Essential for proper nervous system functioning and speed of signal transmission.

Transmission of a Nerve Impulse

1. Resting Membrane Potential: Cell interior is negative relative to the exterior, maintained mainly by Na+/K+ pump.

2. Graded Potential: Changes in membrane potential that can lead to an action potential.

3. Action Potential: Rapid increase followed by decrease in membrane potential; follows all-or-nothing principle.

4. Depolarization: Na+ channels open, allowing Na+ influx, making the inside of the neuron more positive.

5. Repolarization: K+ channels open, K+ leaves the cell, restoring the resting membrane potential.

6. Hyperpolarization: Membrane potential becomes more negative than resting potential due to excess K+ leaving.

7. Refractory Period: A period during which a neuron cannot fire a new action potential; divided into absolute (no response) and relative (requires more stimulation than usual).

Conduction Types

• Saltatory Conduction: Fast transmission where action potentials jump between nodes of Ranvier.

• Continuous Conduction: Slower, occurring in unmyelinated fibers where impulses move smoothly along the membrane.

• All-or-None Law: An action potential either occurs fully or not at all; strength is not proportional to stimulus strength.

Nerve Fiber Types

• Type A Fibers: Thick, myelinated, fastest conduction speeds (motor fibers).

• Type B Fibers: Intermediate diameter, myelinated, moderate conduction speeds.

• Type C Fibers: Thin, unmyelinated, slowest conduction speeds (autonomic fibers).

Synaptic Transmission of Nerve Impulse

1. Synapse: Junction between neurons.

2. Neurotransmitter Release: Chemical signals that transmit nerve impulses across synapses.

3. Excitatory Postsynaptic Potential (EPSP): Depolarization of postsynaptic membrane.

4. Inhibitory Postsynaptic Potential (IPSP): Hyperpolarization of postsynaptic membrane.

5. Summation: Process by which multiple EPSPs or IPSPs combine to influence neuron firing.

6. Facilitation: Increased likelihood of neuron firing due to summation of inputs.

7. Types of Postsynaptic Cells: Target cells receiving neurotransmitter signals (ex: muscle cells, gland cells).

Neurotransmitters Characteristics

• Acetylcholine: Key neurotransmitter in the PNS; involved in muscle contraction and neurotransmission.

• Acetylcholinesterase: Enzyme that breaks down acetylcholine, stopping signal transmission.

• Dopamine: Involved in reward and pleasure pathways, motor control.

• Norepinephrine: Involved in stress response, attention, and mood regulation.

• GABA (Gamma-Aminobutyric Acid): Major inhibitory neurotransmitter in the brain.

• Endorphins: Modulate pain and stress response; part of the body's natural pain relief system.

• Serotonin: Affects mood, sleep cycles, and anxiety regulation.

Importance of the Meninges

• Meninges: Protective coverings of the CNS consisting of three layers:

  • Dura Mater: Tough outer layer protecting the brain and spinal cord.

  • Arachnoid Mater: Middle web-like layer; contains CSF.

  • Pia Mater: Thin inner layer adhering to the surface of the brain and spinal cord.

• Dural Sinuses: Venous blood channels created between the layers of dura mater.

• Epidural Space: Space between dura mater and the bony encasement; contains fat and blood vessels.

• Subarachnoid Space: Contains cerebrospinal fluid (CSF); cushioning the brain and spinal cord.

• Trabeculae: Thin fibers extending between arachnoid and pia mater, helping to anchor the brain.

• Arachnoid Villi (Granulations): Projections into the dural sinuses; involved in CSF absorption.

Components of the Spinal Nerves

• Epineurium: Outer layer enclosing the entire nerve.

• Perineurium: Surrounds groups of nerve fibers (fascicles).

• Endoneurium: Innermost layer; surrounds individual nerve fibers.

Nerve Plexuses and Innervation Areas

• Cervical Plexus: Innervates neck, diaphragm.

• Brachial Plexus: Innervates upper limbs.

• Lumbar Plexus: Innervates lower limbs, pelvic organs.

• Sacral Plexus: Innervates pelvic floor and lower limbs; includes sciatic nerve.

Reflex Arc Components

1. Stimulus: Initiates reflex action.

2. Sensor: Senses the stimulus.

3. Sensory Neuron: Carries impulse to CNS.

4. Interneuron: Processes the signal within the CNS.

5. Motor Neuron: Sends signal to effector.

6. Effector: Muscle or gland that responds to the stimulus.

Reflex Classifications

• Development reflexes:

  innate-developed in the womb; withdrawal (pain), chewing, suckling, object tracking (there’s 27 innate reflexes)

  acquired- learned responses; learned by repetition, stepping on the brake, staying upright when skating

• Site processing reflexes:

  Spinal reflexes- occur in the spinal cord, includes plantar and patellar reflexes.

  Cranial: occur within the brain, loud noises, bright lights

• Nature of response:

  somatic reflexes- immediate, involuntary, vital response of skeletal muscle to prevent injury, falling, slip, trip, sharp injuries.

  Visceral reflexes- AKA autonomic reflexes control all other effectors, coughing, sneezing, vomiting

• Circuit complexity

  monosynaptic reflexes- simple, only 1 neuron involved, patellar and plantar reflexes control

  polysynaptic reflexes- causes muscle stimulation and inhibition, withdrawal reflex and tendon reflex. Stepping on something sharp.

• Reinforcement of Reflexes: Increased efficacy of reflex responses.

• Inhibition of Reflexes: Decreased efficacy or cessation of reflex responses.

Anatomy of the Spinal Cord and Nervous Structures

• Key features of the spinal cord:

  • Posterior Median Sulcus: Groove along back of spinal cord.

  • Dorsal/Ramus: Branches of spinal nerves that serve different regions.

  • Gray Matter and White Matter: Gray matter contains neuron cell bodies (horns); white matter contains myelinated axons (columns).

  • Central Canal: CSF-filled cavity in the center of the spinal cord.

  • Conus Medullaris and Cauda Equina: End of the spinal cord and bundle of spinal nerves respectively.

Brain and Cranial Nerves

• Dura Folds: Structure providing support and separation within the brain (e.g., falx cerebri).

• Gray Matter vs. White Matter: Gray matter contains neuronal cell bodies; white matter consists of myelinated axons.

• Major Brain Parts: Includes Brain Stem, Cerebrum (lobes: frontal, parietal, temporal, occipital), and Cerebellum.

• Cerebrospinal Fluid Flow: Circulates through ventricles and subarachnoid space; nourishes and cushions the brain.

Components of the Limbic System

• Amygdala: Involved in emotions and memory.

• Hippocampus: Critical for learning and memory formation.

• Mammillary Bodies: Involved in memory processing.

• Fornix: Connects hippocampus to other brain structures involved in memory.

EEG and Brain Waves

• Electroencephalogram (EEG): Measures electrical activity in the brain.

• Types of Brain Waves:

  • Delta Waves: Slow waves prominent in deep sleep.

  • Theta Waves: Associated with light sleep and relaxation.

  • Alpha Waves: Present when awake but relaxed.

  • Beta Waves: Associated with active thinking and problem-solving.

Nervous System Disorders to Know

• Alzheimer's Disease: Progressive neurodegeneration characterized by memory loss.

• Epilepsy: Neurological disorder marked by recurrent seizures.

• Multiple Sclerosis (MS): Autoimmune disease affecting the CNS, damaging myelin.

• Polio: Infectious viral disease affecting motor neurons.

• Sciatica: Pain along the sciatic nerve, often due to herniated discs.

• Shingles: Viral infection resulting from reactivation of the chickenpox virus.

• Parkinson's Disease: Neurodegenerative disorder affecting movement, characterized by tremors.

• Meningitis: Inflammation of the protective membranes covering the brain and spinal cord.

• Huntington's Disease: Genetic disorder causing progressive degeneration of nerve cells in the brain.