Nervous System and Special Senses: Study Guide

Nervous System

Overview and Functions

The nervous system is responsible for coordinating the body's response to internal and external stimuli. It is divided into central and peripheral components, each with specialized functions.

• Five Functions of the Nervous System:

  • Sensory input

  • Integration

  • Motor output

  • Homeostasis

  • Mental activity

Divisions of the Nervous System

• CNS (Central Nervous System): Consists of the brain and spinal cord; responsible for processing and integrating information.

• PNS (Peripheral Nervous System): Includes cranial and spinal nerves; transmits sensory information to the CNS and carries motor commands away from the CNS.

• Functional Divisions of the PNS:

  • Sensory (Afferent) Division: Transmits sensory information to the CNS.

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

  • Somatic Nervous System: Controls voluntary movements (skeletal muscle).

  • Autonomic Nervous System: Controls involuntary functions (smooth muscle, cardiac muscle, glands). Subdivided into:

    • Sympathetic Division: "Fight or flight" responses.

    • Parasympathetic Division: "Rest and digest" responses.

Neurons and Neuroglia

• Neurons: The primary cells of the nervous system, specialized for transmitting electrical impulses.

  • Three Main Parts: Cell body (soma), dendrites, axon.

  • Function: Receive, process, and transmit information.

• Neuroglia (Glial Cells): Support, protect, and nourish neurons.

Types of Neurons

• Sensory (Afferent) Neurons: Carry impulses toward the CNS.

• Motor (Efferent) Neurons: Carry impulses away from the CNS to effectors.

• Interneurons: Connect neurons within the CNS.

Myelination and Nerve Impulses

• Myelin Sheath: Insulating layer around axons, increases speed of nerve impulse conduction.

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

• Saltatory Conduction: Action potentials "jump" from node to node, increasing speed.

Action Potentials

• Resting Potential: The electrical charge difference across the membrane of a resting neuron (typically -70 mV).

• Action Potential: A rapid change in membrane potential that travels along the axon.

  • Generated by the movement of Na+ and K+ ions across the membrane.

• Synaptic Transmission: Communication between neurons via neurotransmitters (chemical) or direct electrical connections.

Organization of the Nervous System

• Spinal Nerves: 31 pairs, named and grouped as follows:

  • 8 Cervical

  • 12 Thoracic

  • 5 Lumbar

  • 5 Sacral

  • 1 Coccygeal

• Plexuses: Networks of nerves (cervical, brachial, lumbar, sacral).

Reflexes

• Types of Reflexes:

  • Somatic Reflexes: Involve skeletal muscles.

  • Autonomic Reflexes: Involve smooth muscle, cardiac muscle, or glands.

• Reflex Arc: The pathway followed by nerve impulses during a reflex action.

Meninges and Brain Anatomy

• Meninges: Three protective membranes surrounding the brain and spinal cord:

  • Dura mater (outermost)

  • Arachnoid mater (middle)

  • Pia mater (innermost)

• Brain Regions:

  • Cerebrum

  • Diencephalon

  • Cerebellum

  • Brainstem

Brainstem and Cerebellum

• Brainstem: Includes midbrain, pons, and medulla oblongata; controls vital functions such as breathing and heart rate.

• Cerebellum: Coordinates muscle activity and balance; contains white and gray matter.

Diencephalon

• Thalamus: Sensory relay station.

• Hypothalamus: Regulates homeostasis, including temperature, hunger, and hormone release.

• Epithalamus and Subthalamus: Additional regulatory roles.

Cerebrum

• Lobes: Frontal, parietal, temporal, occipital.

• Functions: Higher cognitive functions, sensory interpretation, voluntary movement.

Limbic System

• Involved in emotion and memory.

Ventricles and Cerebrospinal Fluid (CSF)

• Ventricles: Four interconnected cavities in the brain that produce and contain CSF.

• CSF: Cushions the brain and spinal cord, removes waste, and provides nutrients.

Cranial Nerves

• 12 pairs, each with specific sensory, motor, or mixed functions.

Sensory Receptors and Pathways

• General Senses: Touch, pressure, pain, temperature, proprioception.

• Special Senses: Vision, hearing, taste, smell, equilibrium.

• Types of Sensory Receptors:

  • Mechanoreceptors (touch, pressure)

  • Thermoreceptors (temperature)

  • Photoreceptors (light)

  • Chemoceptors (chemicals)

  • Nociceptors (pain)

• Proprioceptors: Detect body position and movement.

Touch and Proprioception

• Meissner Corpuscles: Detect fine touch and two-point discrimination.

• Merkel Disks: Detect light touch and superficial pressure.

• Hair Follicle Receptors: Detect hair movement.

Speech and Language Areas

• Broca's Area: Motor speech area; controls movements required for speech.

• Wernicke's Area: Language comprehension.

Memory

• Types of Memory:

  • Short-term memory

  • Long-term memory

  • Working memory

• Memory Storage: Different brain regions are involved in different types of memory.

Special Senses

Vision

• Three Layers of the Eye:

  • Fibrous (sclera and cornea)

  • Vascular (choroid, ciliary body, iris)

  • Nervous (retina)

• Parts of the Eye: Cornea, lens, retina, optic nerve, aqueous and vitreous humors.

• Pupil: Regulates the amount of light entering the eye.

• Retina: Contains photoreceptors (rods and cones) for vision.

• Optic Nerve: Transmits visual information to the brain.

Hearing and Equilibrium

• Ear Anatomy: Outer, middle, and inner ear.

• Organ of Corti: Contains hair cells that detect sound vibrations.

• Semicircular Canals: Detect rotational movement (equilibrium).

Taste and Smell

• Taste Buds: Contain receptors for five basic tastes (sweet, sour, bitter, salty, umami).

• Olfactory Receptors: Detect odor molecules; located in the nasal cavity.

Summary Table: Types of Sensory Receptors

Receptor Type	Stimulus Detected	Example Location
Mechanoreceptor	Touch, pressure, vibration	Skin, ear
Thermoreceptor	Temperature	Skin
Photoreceptor	Light	Retina
Chemoceptor	Chemicals	Taste buds, olfactory epithelium
Nociceptor	Pain	Throughout body
Proprioceptor	Body position, movement	Muscles, tendons, joints

Additional info:

• Action potentials are described by the equation: $V_m = V_{rest} + ext{change in membrane potential}$

• Saltatory conduction is faster than continuous conduction due to myelination.

• Broca's and Wernicke's areas are typically located in the left hemisphere of the brain.