Human Anatomy and Physiology Exam 3

Whole body communication

Our body sends messages across tissues and organs to coordinate homeostatic responses through the nervous and endocrine system

The nervous system

The primary coordinating and controlling system of the body (Uses action potentials and neurotransmitters to communicate)

Nervous system functions

• Detect internal and external changes

• Analysis of detected changes

• Organization of information

• Initiation of appropriate actions

Anatomical Divisions of the nervous system

Central Nervous System (CNS), Peripheral Nervous System (PNS), Sensory Division (part of PNS), and Motor Division (part of PNS)

Central Nervous System (CNS)

Brain and spinal cord, receives action potentials, analyzes and organizes it, then initiates appropriate action

• Produced by Oligodendrocytes

Peripheral Nervous System (PNS)

(Located outside the CNS)

• Cranial and spinal nerves, ganglia, sensory receptors, and effectors

• Carries action potentials formed by sensory receptors, to the CNS

• Also carries action potentials from the CNS to the effectors

• Produced by Schwann cells

Sensory Division (afferent division)

(PNS signals going to the CNS)

• Somatic (skeletal muscle) sensory information (body)

• Visceral (cardiac/smooth muscle and glands) sensory information

Motor Division (efferent division)

(CNS sending signals/commands to the PNS)

• Somatic motor division (skeletal muscle)

• Autonomic/visceral motor division (viscera) (involuntary)

Somatic motor division (skeletal muscle)

Somatic = skeletal muscle neurons: motor neurons (voluntary/involuntary control)

Autonomic/visceral motor division (viscera) (involuntary)

Visceral = automatic nervous system: parasympathetic and sympathetic 

Neuron

• Structural and functional unit of nervous system

• Specialized to generate and transmit action potentials

Neuron features

1. Dendrites

2. Neuron Cell Body

3. Axon

Dendrites

receiving end, gathers info, carries impulses toward cell body/axon

Neuron Cell Body (aka soma)

nucleus and organelles, integration of info

Axon

output, carries signal over long distances

• Only 1 in a neuron

• Located at the end of the neuron

• Sending portion of the electrical signal

Myelin Sheath

Made by neuroglia (supporting cells) = allows faster conduction when present 

Multipolar neuron

• Most common

• Several dendrites, single axon

• Motor neurons

• Interneurons

Bipolar neuron

• One dendrite and one axon 

• Rare; in some special senses

Pseudounipolar neuron

• Single process

• Sensory neurons

Neuroglia

• Function: support and protect neurons

• More numerous than neurons

• Make up the Myelin Sheath

Schwann cells (PNS)

• They wrap around length of axon

• Multiple schwann cells per one axon

• Allows for regeneration of nervous tissue

• Essential for axon regeneration

Oligodendrocytes (CNS)

• One oligodendrocytes per multiple axons 

• Suppresses regeneration of nervous tissue

• Forms myelin sheath

• Does not form neurilemma

• Axon regeneration is not possible

Bones (protection for the CNS)

• Cranial bones: protect the brain

• Vertebrae: protect the spinal cord

 Meninges (protection for the CNS)

Three membranes arranged in layers surrounding brain and spinal cord

 Meninges from innermost to outermost layers

• Pia mater, thin, innermost

• Arachnoid mater, Middle layer

• Dura mater, Thick, outermost

Pia mater

Thin, nourishes brain and spinal cord

Arachnoid mater

Shock absorber for the brain and spinal cord

Dura mater

Thick, protective cushion for the brain and spinal cord

Neural Communication

1. Irritability

2. Conductivity

Irritability (neural communication)

 Ability to respond to a stimulus by forming an action potential (electrical signal)

Conductivity (neural communication)

Ability to transmit action potentials along an axon to other neurons or effector cells

Plasma membrane review

• Function: Separates intracellular fluid (ICF) and extracellular fluid (ECF)

• Sodium (Na+) and Potassium (K+)

• Structure: Proteins: transport across cell membrane through channels and carriers

Membrane Potential in Neurons

• Electrical charge difference across the plasma membrane is due to an unequal ion distribution = membrane potential

• In inactive irritable cells this is called resting membrane potential (RMP) ( -70mv)

• Potassium on the inside of the cell and Sodium on the outside

Resting Membrane Potential

• ECF: high sodium (Na+) and chlorine (Cl−), low  potassium (K+)

• Cytosol (ICF): low sodium (Na+) and chlorine (Cl−) , high potassium (K+)

• Net excess of “+” charges on the ECF-side

• Net excess of “-” charges on the cytosol-side

Action Potentials

Change in membrane potential that is conducted to the terminal bouton

• Threshold stimulus is needed to activate a neuron to produce an action potential

• All action potentials are identical, meaning change in membrane potential is always the same (all-or-none response)

Action Potential Steps

1. With a threshold stimulus, voltage gates sodium channels open

2. Sodium enters

3. Voltage gated potassium channels open

4. Potassium diffuses out

Depolarization

After reaching threshold voltage, depolarization occurs

1. Voltage-gate opened with an electrical signal

2. Sodium enters the cell

3. Voltage-gated Na+ channels open, Na+ diffuses into the neuron

4. -70 mv (at rest) + new positive ions entering the cell = decreasing negativity (depolarization) until +30 (max.) is reached, then channel closes

Repolarization

1. Immediately after depolarization, Na+ channels close and K+ channels open → K+ diffuses out of the neuron

• Potassium inside the cell leaves 

2. Membrane repolarizes

• Potassium (K+) loss to ECF allows voltage to change from +30 mV back to -70 mV

Synapse

Junction of one axon with another neuron or an effector cell (ex. neurotransmitter junction)

Synaptic transmission

Conversion of electrical signals (action potentials) into chemical signals (neurotransmitters) at a synapse in order to relay physiological information to another cell

Presynaptic neuron

Has the information for the synaptic transmission

Postsynaptic structure

Receives the information for the synaptic transmission

Synaptic cleft

Location of transfer of information in synaptic transmission

Steps of Synaptic Transmission

1. Action potential travels along the axon to reach the terminal bouton (synapse)

2. Terminal bouton releases neurotransmitters into the synaptic cleft

3. Neurotransmitters (gated ion channels) diffuse

4. Neurotransmitters bind to receptors on the postsynaptic (neuron) plasma membrane

Synapse Events

Signal transmission occurs in only one direction

• Only terminal boutons release neurotransmitters

Neurotransmitters are quickly removed from synapse

• Diffuse away, reabsorbed, decomposed by enzymes

• Prevents continuous stimulation or inhibition of postsynaptic neuron or effector

Excitatory

sodium enters cell, sodium channels open

Inhibitory

chlorine enters cell, chlorine channels open, makes cell more negative and no action potential is sent

The outer layer of the brain is composed of grey matter and is called

 the cerebral cortex

Several masses of grey matter are called

basal nuclei

Fold/ridges of the brain are called

cerebral gyri (gyrus)

Shallow grooves between gyri are called

cerebral sucli (sulcus)

Fissures of the brain

deep, prominent grooves in the cerebral cortex that divide the brain into functional lobes and hemispheres

Descending (motor) tracts

carry action potentials to the brain

Ascending (sensory) tracts

carry action potentials from the brain

Four major components of the brain

1. Cerebrum (frontal, parietal, occipital)

2. Cerebellum

3. Diencephalon

4. Brainstem

Gray matter consists of

cell bodies

White matter consists of

myelinated axons

Gray brain matter functions

• Perception of sensations

• Voluntary actions

• Reasoning

• Planning

• Problem solving

Hemispheres

• Connected by the corpus callosum

• Separated by the longitudinal cerebral fissure

Cerebral hemisphere five lobes

1. Frontal lobe

2. Parietal lobe

3. Occipital lobe

4. Temporal lobe

5. Insula (lies underneath the lateral sulcus)

The cerebrum has 3 types of functional areas:

1. Sensory areas

2. Motor areas

3. Association areas

 Sensory Areas

Receive action potentials from sensors receptors and interpret them as sensations

 Motor Areas

• Located in frontal lobe

• Contralateral representation occurs

• If damaged: can understand speech, but has a hard time speaking or replying

 Association areas

communication between sensory inputs and motor outputs

• Role in interpretation of sensations and coordination of motor responses

• If damaged: can not understand speech, but can talk fine (can’t read either)

Left hemisphere functions

• analytical and verbal skills (in 90% of population)

  • Posterior language area: temporal and parietal lobes of only one hemisphere

  • Motor speech area: near lower end of precentral gyrus in only one hemisphere

Right hemisphere functions

•  musical, artistic and spatial awareness, imagination, and insight

Diencephalon

Lies between the brainstem and cerebrum

Diencephalon brain areas

1. Thalamus

2. Hypothalamus

3. Epithalamus

Thalamus

• Receives all incoming sensory action potentials (except smell) and relays them to the cerebral cortex

• Part of the circuitry that influences movement

Hypothalamus

Primary function is the maintenance of homeostasis

• Major integration center for the autonomic division

• Connecting link between brain and endocrine system

• Controls the pituitary gland

• Plays a critical role in connecting the nervous system to the endocrine system through its influence on the pituitary gland

Epithalamus

• Located behind the thalamus

• Forms part of the roof of the third ventricle

• Contains the pineal gland

Limbic System

• Involved in memory, emotions, and emotional behavior

• Regulates emotional behavior, especially behavior that enhances survival

pineal gland

• Produces the hormone melatonin when sunlight levels are low

• Induces sleepiness

• May assist in regulating onset of puberty

Brain stem

• Stalk-like portion connecting higher brain centers with the spinal cord

• Contains nuclei surrounded by white matter

Brain stem areas

1. Midbrain

2. Pons

3. Medulla oblongata

 Midbrain

• Located posterior to hypothalamus, superior to pons

• Reflex centers for movements in response to visual and auditory stimuli

• Contains substantia nigra, which communicates with basal ganglia via neurotransmitter dopamine

Pons

• Between midbrain and medulla oblongata

• Primarily contains axons (gray matter)

• Controls coughing, blood pressure, heart rate, and breathing

Medulla Oblongata

Most inferior portion of the brain that connects to the spinal cord

Medulla Oblongata integration centers

1. Respiratory rhythmicity center

• Regulates basic rhythm of breathing

• Reflexes like coughing and breathing

2. Cardiac control center

• Regulates rate and force of heart contractions

3. Vasomotor center

• Regulates blood pressure and blood flow

Reticular Formation (brain stem)

• Extending from the upper spinal cord, through the brainstem, and into the diencephalon

• Arouses the cerebrum to wakefulness

• A decrease in activity results in sleep

• Damage can cause unconsciousness or coma

Cerebellum

• Second largest brain region

• Contains an outer layer of grey matter surrounding the white matter underneath

Cerebellum location

• Upper surface separated from the occipital and temporal lobes by the transverse cerebral fissure

• Two hemispheres connected by the vermis

Cerebellum function

• Controls and coordinates the interaction of skeletal muscles (fine motor skills)

• Controls posture, balance, and muscle coordination during movement

• Damage results in loss of equilibrium, muscle coordination, and muscle tone

Cerebrospinal Fluid

• Shock absorber for brain and spinal cord

• Transportation of ions, nutrients, and wastes

• Provides buoyancy (“Floats” the brain and prevents contact with cranial floor)

The brains four interconnecting ventricles

• Two lateral ventricles (Left and Right)

• Third ventricle (First on the midline)

• Fourth ventricle (Last on the midline)

Spinal cord

• Descends from medulla oblongata through foramen magnum

• Passes through vertebral canal to level of 2nd lumbar vertebra

• Gives rise to 31 pairs of spinal nerves

Spinal cord divisions

1. Cervical

2. Thoracic

3. Lumbar

4. Sacral

Posterior horn of the spine is also called

Dorsal horn

Anterior horn of the spine is also called

ventral horn

Peripheral Nervous System (PNS)

• Consists of cranial nerves and spinal nerves that connect the CNS to parts of the body

• A nerve is a bundle of axons bound together by connective tissue

  • Motor nerves

  • Sensory nerves

  • Mixed nerves

• Nerves can contain both somatic axons (for skeletal muscle) and autonomic axons (for visceral organ structures)

Somatic axons are used for

skeletal muscles

autonomic axons are used for

visceral organ structures

Motor nerves are used for

movement

Sensory nerves are used for

gathering information

Mixed nerves are used for

Both motor and sensor functions

Ascending tracts relate to

Sensory

Descending tracts relate to

Motor/movement

Cranial nerves

• 12 pairs of nerves

• Arise from brain, connect primarily with structures in head and neck

• Most arise from the brainstem

• Five are primarily motor, three are sensory, four are mixed

CNI (1)

Olfactory, smell

CNII (2)

Optic nerve, sight