BIO 141: Nervous System Study Guide (Chapters 11-13)

Nervous Tissue and Nervous System

Classification of the Nervous System

The nervous system is a complex network responsible for coordinating body activities. It is divided into two major parts:

• Central Nervous System (CNS): Consists of the brain and spinal cord. It acts as the main control center for processing information.

• Peripheral Nervous System (PNS): Composed of all neural tissue outside the CNS, including nerves and ganglia. It connects the CNS to limbs and organs.

Organs of the CNS and PNS

• CNS: Brain and spinal cord.

• PNS: Cranial nerves (12 pairs), spinal nerves (31 pairs), ganglia, and sensory receptors.

Types of Nerves

• Cranial Nerves: 12 pairs, emerge from the brain.

• Spinal Nerves: 31 pairs, emerge from the spinal cord.

Characteristics of Neurons

• Excitable cells that transmit electrical signals.

• Long-lived, amitotic (do not divide), and have a high metabolic rate.

• Specialized for communication via action potentials and neurotransmitters.

Major Parts of a Neuron and Their Functions

• Cell Body (Soma): Contains the nucleus and organelles; metabolic center.

• Dendrites: Receive incoming signals from other neurons.

• Axon: Conducts electrical impulses away from the cell body.

Major Parts of an Axon

• Axon Hillock: Initiates action potentials.

• Axon Terminals: Release neurotransmitters to communicate with other cells.

• Myelin Sheath: Insulating layer that increases the speed of impulse conduction.

• Nodes of Ranvier: Gaps in the myelin sheath where action potentials are regenerated.

Function of Myelin Sheath

• Insulates axons, allowing for faster transmission of electrical impulses (saltatory conduction).

• Produced by oligodendrocytes in the CNS and Schwann cells in the PNS.

Myelinated vs. Unmyelinated Axons

• Myelinated Axons: Conduct impulses rapidly due to saltatory conduction.

• Unmyelinated Axons: Conduct impulses more slowly via continuous conduction.

Gray Matter vs. White Matter in the Brain

• Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons; located on the outer surface (cortex) of the brain and inner part of the spinal cord.

• White Matter: Composed mainly of myelinated axons; found deeper in the brain and outer part of the spinal cord.

Axon Diameter and Speed of Impulse Propagation

• Larger diameter axons conduct impulses faster due to lower resistance to current flow.

• Speed is also increased by myelination.

Repair in CNS vs. PNS

• CNS: Limited ability to repair due to inhibitory factors and lack of growth-promoting environment.

• PNS: Schwann cells promote axon regeneration, allowing some repair after injury.

The Central Nervous System (CNS)

Functions of the CNS

• Integrates sensory information and coordinates voluntary and involuntary responses.

• Responsible for higher functions such as thought, memory, and emotion.

Major Parts of the Brain

• Cerebrum: Largest part; responsible for higher brain functions.

• Diencephalon: Includes thalamus and hypothalamus; relays sensory information and controls autonomic functions.

• Brain Stem: Includes midbrain, pons, and medulla oblongata; controls basic life functions.

• Cerebellum: Coordinates movement and balance.

Protection of the CNS

• Bony Protection: Skull protects the brain; vertebral column protects the spinal cord.

• Meninges: Three connective tissue layers (dura mater, arachnoid mater, pia mater) surround the CNS.

• Cerebrospinal Fluid (CSF): Cushions and nourishes the CNS.

• Blood-Brain Barrier: Regulates passage of substances from blood into the brain.

Space Containing CSF

• Subarachnoid Space: Located between the arachnoid mater and pia mater; filled with CSF.

Importance of Sufficient Blood Flow in the Brain

• Ensures delivery of oxygen and nutrients; lack of blood flow can cause brain damage within minutes.

Blood-Brain Barrier

• A selective barrier formed by endothelial cells of brain capillaries; protects the brain from harmful substances.

Cerebrospinal Fluid (CSF)

• Definition: Clear, colorless fluid produced by the choroid plexus.

• Functions: Cushions the brain, removes waste, and provides nutrients.

• Characteristics: Low protein, few cells, similar to plasma but with different ion concentrations.

Brain Surface Features

• Gyrus (plural: Gyri): Elevated ridges on the brain surface.

• Sulcus (plural: Sulci): Shallow grooves between gyri.

• Fissure: Deep grooves that separate large brain regions.

Lobes of the Cerebrum

• Frontal, Parietal, Temporal, Occipital, and Insula (deep within the lateral sulcus).

Sensory, Motor, and Association Areas in the Cerebrum

• Sensory Areas: Receive and interpret sensory information.

• Motor Areas: Control voluntary muscle movements.

• Association Areas: Integrate information for complex functions (e.g., reasoning, language).

Association Areas and Their Functions

• Prefrontal Cortex: Planning, decision-making, personality.

• Wernicke's Area: Language comprehension.

• Broca's Area: Speech production.

Major Parts of the Diencephalon and Their Functions

• Thalamus: Relay station for sensory information.

• Hypothalamus: Regulates homeostasis, endocrine functions, and autonomic nervous system.

• Epithalamus: Contains pineal gland; involved in sleep-wake cycles.

Parts of the Brain Stem and Their Functions

• Midbrain: Visual and auditory reflexes.

• Pons: Relays information between cerebrum and cerebellum; regulates breathing.

• Medulla Oblongata: Controls vital functions (heart rate, breathing, blood pressure).

Functions and Major Parts of the Cerebellum

• Functions: Coordinates voluntary movements, balance, and posture.

• Major Parts: Two hemispheres, vermis (central region), and cerebellar cortex.

Functions of the Spinal Cord

• Conducts sensory and motor information between the body and brain.

• Integrates reflexes.

Sensory vs. Motor Tracts in the Spinal Cord

• Sensory (Ascending) Tracts: Carry sensory information to the brain.

• Motor (Descending) Tracts: Carry motor commands from the brain to the body.

The Peripheral Nervous System (PNS)

Spinal Nerve Plexuses

• Cervical Plexus: Supplies neck and diaphragm.

• Brachial Plexus: Supplies upper limbs.

• Lumbar Plexus: Supplies lower abdomen and thigh.

• Sacral Plexus: Supplies pelvis and lower limbs.

Reflexes

• Definition: Rapid, automatic response to a stimulus.

• Example: Knee-jerk (patellar) reflex.

Cranial Nerves: Numbers, Names, Types, and Functions

Number	Name	Type	Function
I	Olfactory	Sensory	Smell
II	Optic	Sensory	Vision
III	Oculomotor	Motor	Eye movement, pupil constriction
IV	Trochlear	Motor	Eye movement
V	Trigeminal	Both	Facial sensation, chewing
VI	Abducens	Motor	Eye movement
VII	Facial	Both	Facial expression, taste
VIII	Vestibulocochlear	Sensory	Hearing, balance
IX	Glossopharyngeal	Both	Taste, swallowing
X	Vagus	Both	Visceral sensation, parasympathetic control
XI	Accessory	Motor	Head and shoulder movement
XII	Hypoglossal	Motor	Tongue movement

Sensation vs. Perception

• Sensation: Detection of stimuli by sensory receptors.

• Perception: Interpretation of sensory information by the brain.

Touch and Pressure Receptors

• Meissner's Corpuscles: Detect light touch.

• Pacinian Corpuscles: Detect deep pressure and vibration.

• Merkel Discs: Detect steady pressure.

Referred Pain

• Definition: Pain perceived at a location other than the site of the painful stimulus, due to shared neural pathways.

• Example: Pain from a heart attack felt in the left arm.

Proprioception and Proprioceptors

• Proprioception: Sense of body position and movement.

• Proprioceptors: Sensory receptors located in muscles, tendons, and joints.

Additional info: Some explanations and examples have been expanded for clarity and completeness.