Biology Test 2

Nervous System Function

Integrates and coordinates the body’s activities

The Central Nervous System

The Brain and spinal cord

Peripheral nervous system

Nervous tissue outside the CNS

Nervous system composition

Neurons and Neuroglial cells

Neurons

Excitable cells that generates and transmits messages

Neuroglial cells

Several types of them, each with a special function, including providing structural support, growth factors, and isolating sheaths around axons. Outnumbers neurons 10 to 1

The categories of neurons

Sensory, Motor, and Interneurons

Sensory neurons

Carries information toward the CNS from sensory receptors

Motor Neurons

Carry information away from the CNS to an effector either a muscle or gland

Interneurons

Found only in the brain and spinal cord, between sensory and motor neurons, Integrate and interpret sensory signals

Dendrites

Receives signals from other cells, carry information toward the cell body

Axon

Carries information away from the cell body to either another neuron or an effector

Cell body

Contains nucleus and other organelles, functions to maintain the neuron

Myelin Sheath

Found on most axon outside the CNS and some within the CNS, increases the rate of conduction of a nerve impulse

Schwann cells

A type of glial cell that form the myelin sheath

Nodes of Ranvier

Gaps between the Schwann cells.

Saltatory Conduction

Messages travel faster as they jump from node to node

Multiple Sclerosis

A disease in which the myelin sheaths in the brain and spinal cord are progressively destroyed

Nerve Impulses

An electrochemical signal involving sodium and potassium ions that cross the cell membrane through ion channels

Ion Channels vs Sodium-Potassium pumps

Ion channels do not require energy, sodium-potassium pumps do require energy

Depolarization

Reduction of the charge difference across the membrane. Due to the rush of sodium ions inside

Repolarization

Restoration of the charge difference across the membrane. Due to the move of potassium out of the axon

Synapse

a junction between a neuron and another cell

Neurotransmitters

Communication between a neuron and an adjacent cell

Synaptic Cleft

Gap between two cells, Neurotransmitters diffuse across the gap

Synaptic Knob

Swelling at the end of a presynaptic neuron

Synaptic transmission process

1. The nerve impulse reaches the synaptic knob of the end of the presynaptic cleft

2. Calcium ions move into the synaptic knob which releases the neurotransmitter into the synaptic cleft

3. The neurotransmitter diffuses across the synaptic cleft and binds with receptors on the membrane of the postsynaptic neuron, causing an ion channel to open

Excitatory synapse

binding of the neurotransmitter to the receptor causes sodium channels to open, increasing the likelihood that an action potential will begin

Inhibitory synapse

Binding of the neurotransmitter to the receptor opens different ion channels

Neurotransmitter examples

Acetylcholine: Found both in the PNS and CNS, released in every neuromuscular junction

Norepinephrine: Regulates mood, hunger, thirst, sex drive

Serotonin: Promotes a feeling of well-being

Dopamine: regulates emotions and complex movements

Myasthenia Gravis

autoimmune disease that attacks the acetylcholine receptors at neuromuscular junctions, resulting in little muscle strength

Alzheimer’s disease

Associated with decreased levels of acetylcholine

Clinical depression

Associated with decreased levels of serotonin, dopamine, and norepinephrine

Parkinson’s disease

associated with decreased levels of dopamine

CNS (Central nervous system)

Consists of the brain and spinal cord. Integrates incoming information and coordinates all voluntary and involuntary nervous functions

PNS (Peripheral nervous system)

Consist of ganglia and the nerves that branch from the CNS. Keeps the CNS in contact with the rest of the body

Somatic nervous system

recives sensory information and directs voluntary movements

Automatic nervous systems

regulates involuntary activities

Sympathetic nervous system

in charge during emergencies. Prepares the body for fight-or-flight

Parasympathetic nervous system

in charge during restful times. conserves energy during restful times

Protection of the CNS

Bones of the skulls and the vertebral colum

The Meninges

1. Dura mater - outermost layer

2. Arachnoid - middle layer

   1. Pia mater - innermost layer

Meningitis

inflammation of the meninges is caused by bacteria and viruses and can lead to inflammation of the brain

Cerebrospinal fluid

Fills space between the meninges, internal cavities of the brain or ventricles, and the cavity of the spinal cord or the central canal

Cerebrospinal fluid functions

• Shock absorption

• Support

• Nourishment and waste removal

Blood-brain barrier

formed by right junctions between cells in the walls of capillaries supplying the CNS

Blood-brain barrier functions

• Protection the CNS by selecting the substances that can enter the cerebrospinal fluid from the blood

  • Can inhibit many potentially life-saving, infection-fighting, or tumor-suppressing drugs from reaching brain tissue if they are not lipid soluble

Cerebrum

The thinking, conscious part of the brain that accounts for 83 percent of total brain weight

The two hemispheres

Each receive sensory information from and directs movements of the opposite side of the body

Cerebral Cortex

Thin outer layer. Outer layer made of gray matter. White matter is the layer beneath

Midbrain

Relays on information bwtween cerebellum and spinal cord. Intergrates sensory input

Pons

A bridge between higher and lower brain centers

Medulla oblongata

Contains automatic centers for heart rates and digestive activates. Relays on sensory information to thalamus

Cerebellum

Coordinates sensory-motor voluntary movements. Stores memory of learned motor patterns

Cerebrum

Contains sensory areas for skin senses, vision, hearing, and smell. Motor areas for voluntary control of movement. Interprets language, thinking, decision making, self-awareness, creativity, and storage of memories.

Corpus callosum

Allows left and right cerebral hemisphere to communicate with one another. Band of white matter.

Thalamus

Process all sensory information except smell. Relays information to appropriate higher brain centers

Hypothalamus

controls heart rate, blood pressure, breathing rate, body temperature, food intake, and emotions

Gray matter

includes neuroglial cells, nerve cell bodies, and unmyelinated axons

White matter

consist of myelinated axons allows for communication between various areas of the brain, and between the brain and spinal cord

Lobes of the brain

• Frontal lobe

• Parietal lobe

• Temporal lobe

• Occupational lobe

Parts of the brain

Sensory, motor and association

Sensory areas

Primary somatosensory area receives sensory information from the body

Motor areas

• Primary motor areas controls the skeletal muscles

  • Premotor cortex coordinates learned motor skills

Association areas

Communicate with the sensory area, motor areas, and other parts of the brain to analyze and act on sensory input

Prefrontal cortex

enables us to reason and think

Limbic system

• Defined on the basis of function rather than autonomy

• Includes several brain structures that produce emotions and memory

Short-term memory

holds a small amount of information for a few seconds or minutes

Long-term memory

stores limitless amounts of information for hours, days, or years

Reticular activating system

• An extensive network of neurons that runs through the medulla and projects to the cerebral cortex

  • Filters sensory input and keeps the cerebral cortex in an alert state

Spinal Cord

Conducts messages between the brain and the body. Serves as a reflex center

Spinal cord structure

Tube of neural tissue with a central canal inside, protected by stacked vertebrae of the vertebral column, white matter toward surface; gray matter in center

Reflexive arc

A reflex is an automatic response to a stimulus in a pre-wired circuit

Parts of the reflexive arc

1. Receptor

2. Sensory neuron

3. Interneuron

4. Motor Neuron

   1. Effector

Spinal reflexes

decisions made by the spinal cord when a speedy reaction is safer

Spinal nerves

31 pairs, all carry both sensory and motor fibers. Sensory fibers enter the dorsal side of the spinal cord in a bundle called the dorsal root. Axons of motor neurons leave the ventral side of the spinal cord in a bundle called the ventral root

Cranial nerves

12 pairs, service the structures of the head and certain body parts including the heart and diaphragm. Some carry only sensory fibers, others carry only motor fibers, and still others carry both types of fibers

Somatic nervous system

governs conscious sensation and voluntary movements

Automatic nervous system

governs unconscious involuntary internal activates

Headaches

Tension headaches, caused by muscle contraction in the head, face, and neck

Migraine headaches: causes by an imbalance in the brain’s chemistry

Low levels of serotonin

Stroke

Caused by an interruption of blood flow to a region o the brain, resulting in death of nerves

Coma

Caused by trauma to neurons in regions of the brain responsible for stimulating the cerebrum. Person is unresponsive to all sensory input and cannot be awakened

Spinal cord injury

Results in loss of function below site of injury. Depending on which nerves tracts are damaged, injurt may result in paralysis, loss of sensation, or both

Sensory Receptors

Structures that are specialized to detect and respond to changes in the external or internal environment

Categories of sensory receptors

• Mechanoreceptors

• Thermoreceptors

• Photoreceptors

• Chemoreceptors

• Pain receptors

Sensory adaptation

Sensory receptors stop responding when continuously stimulated, leading to a decrease in the awareness of the stimulus

General Senses

touch, pressure, vibration, temperature, body and limb position, and pain. We are not usually aware of general senses.

Special senses

Vision, hearing, equilibrium, smell, and taste. We rely on senses to perceive the world

Special vs General senses

Special Senses: Receptors for the special senses are located in the head, often within specific structures.

General Senses: Receptors located in skin, muscles, bones, joints, and internal organs

Mechanoreceptors

Merkel Disk: free nerve endings that end on Merkel cells, detecting light touch

Meissner’s Corpuscles: Encapsulated nerve endings, tell us where we have been touched

Pacinian corpuscles: layers of tissue surrounding a nerve ending, sense first pressure or vibration

Ruffini corpuscles: encapsulated nerve endings, respond to continuous pressure

Thermoreceptors

Respond to temperature changes

Glaucoma

Second leading cause of blindness. Results when drainage of the aqueous humor is blocked. Pressure within the eye reaches dangerous levels, blood vessels supply the optic nerve and retina collapse and cells die

Cataracts

A lens that has become cloudy, usually due to aging