Nervous System, Spinal Cord, Brain, & Senses

Organization of Nervous System

Central Nervous System

Peripheral Nervous System

Central Nervous System

Brain

Spinal Cord

Peripheral Nervous System

Cranial Nerves

Spinal Nerves

Ganglia (Swelling)

Functions of Nervous System:

Sensory Division

Motor Division

Somatic Sensory

Visceral Sensory

Somatic Motor

Autonomic Motor

Sensory Division

Receives sensory information from receptors and transmits this information to the CNS

Motor Division

Transmits motor impulses from the CNS to muscles or glands

Somatic Sensory

Input received from body (eyes, ears, skin)

Visceral Sensory

Input received from internal organs

Somatic Motor

Output transmitted to skeletal muscles

Autonomic Motor

Output transmitted to involuntary muscle (cardiac & smooth) and glands

Neurons

Excitable cells that initiate and transmit nerve impulses

Glial Cells

Non-excitable cells that support and protect the neurons

Neuron

A nerve cell

Cell Body

Control center for receiving, integrating (processing) & nerve impulses

Nissl Bodies

Chromatophilic substance made of ribosomal RNA & rough ER (makes proteins necessary for cell use and its high metabolism)

Dendrites

Processes that receive information stimuli

Axon

Processes that transmits impulses away from cell body

Neuron Structure

Cell Body

Dendrites

Axon

Neuron Structural Classification

Unipolar

Bipolar

Multipolar

Unipolar

One nerve fiber that divides into one dendrite portion and one (double) axon portion

Bipolar

Two nerve fibers; one dendrite, one axon

Multipolar

Many dendrites, one axon

Neuron Functional Classification

Sensory Neurons

Interneurons

Motor Neurons

Sensory Neurons

(afferent) transmits impulses from receptors to CNS

Interneurons

(association) relay neurons which exist within CNS

Motor Neurons

(efferent) transmits impulses from CNS to receptors

Glial Cells of CNS

Astrocytes

Ependymal Cells

Microglia

Oligodendrocytes

Astrocytes

Structural support & helps form blood-brain barrier

Ependymal Cells

Lines inside of brain ventricles

Microglia

Phagocytizes pathogens & cellular debris

Oligodendrocytes

Myelinates neurons in the CNS

Oligodendrocytes

Accomplishes myelination in the CNS

Neurolemmocytes

Accomplishes myelination in the PNS

Schwann Cells (neurolemmocytes)

Wrap around axon (100x times)

About 1mm long

Composed of Myelin

Sometimes called the myelin sheath

Neurilemma

The outer layer of the Schwann cell containing the nucleus & cytoplasm

Not Continuous

Has neurofibril nodes (nodes of ranvier)

Advantages of the myelin sheath

1. Electrically insulates the neuron

2. Increases speed of the neuron (200x) by Saltatory Conduction

Saltatory Conduction

When the impulse leaps from one neurofibril node to another neurofibril node instead of moving heel-to-toe along the entire axon

Axon Regeneration

Schwann cells are needed for regeneration. Explains why regeneration does not occur in the CNS. CNS only has oligodendrocytes needed for myelin production.

Converging Circuit

Several neurons send impulse to fewer (same neuron)

Diverging Circuit

One (few) neuron(s) sends impulse to many

Spinal Cord

Enclosed within the vertebral canal

Has nerves exiting sides

16-18 inches in length

Groups of axons called the cauda equina

Gray Matter

Unmyelinated neurons

Shape resembles letter H or butterfly

White matter

Myelinated tracts

• Ascending tracts transmits up sensory information

• Descending tracts transmits down motor information

Reflex

An automatic, involuntary response to a stimulus

Involuntary Actions

Heart Rate

Breathing Rate

Blood Pressure

Digestion

Automatic Actions

Coughing

Sneezing

Swallowing

Vomiting

Stretching Reflex

We trick our bodies into thinking we are falling over backwards

Withdrawal Reflex

Caused by pain stimulus

Neuronal Pools

Neurons organized into specific pathways

Meninges

Protective membranes of brain and spinal cord

1. Dura Mater

2. Arachnoid

3. Pia Mater

Dura Mater

Outermost, tough, fibrous CT

Arachnoid

Thin, net-like membrane

Pia Mater

Delicate, loose CT, that helps nourish cells of brain & spinal cord

Ventricles

Four cavities in the brain filled with cerebrospinal fluid

Ventricles Functions

1. Brings nutrients to and takes away wastes from the brain cells

2. Protection

Blood Brain Barrier

Tight junctions between adjacent endothelial cells that don’t allow material to diffuse between cells out of the capillary. Astrocytes wrap around (and completely enclose) capillaries so that any substance that can diffuse through the capillary wall must also diffuse through the astrocyte to get to the brain.

Cerebrum

Two large hemispheres connect by the Corpus Callosum

Corpus Callosum

Connects both halves of the brain and allows communication

Surface of brain contains

Gyri (gyrus)

Sulci (sulcus)

Gryi (Gyrus)

Folds

Sulci (Sulcus)

Grooves

Cerebral Cortex

Thin, gray matter layer on the surface of the brain that goes in and out of the grooves. Provides a larger surface area for neuron dendrites, cell bodies, and unmyelinated neurons. More neuronal connections enhance cognitive processes

Lobes

1. Frontal

2. Parietal

3. Temporal

4. Occipital

5. Insula

Frontal Lobe

1. Intellectual Functions: reasoning & planning

2. Personality: Phineas Cage

3. Verbal Communication: Motor speech area (Broca’s area) controls muscular movements for talking

4. Primary Motor Cortex: in the precentral gyrus, neurons send impulses to voluntary muscles

Parietal Lobe

1. Primary somatosensory cortex (in post central gyrus) senses skins: touch, pain, & temperature

2. Wernicke’s Area

Wernickes Area

Understanding speech and formulating words

Temporal Lobe

Interpretation of auditory and olfactory sensations

Occipital Lobe

Vision

Insula Lobe

Interpretation of taste, emotions, and self-awareness

Association Areas

Connects sensory and motor “cortical areas in all areas of the brain

Interprets incoming information → coordinates response

Diencephalon

1. Epithalamus

2. Thalamus

3. Hypothalamus

Epithalamus

Contains pineal gland

Thalamus

Relay station for sensory impulses (hot chocolate)

• relay station for sensory impulses

• information filter suppresses non-important information

Hypothalamus

Heart Rate

Blood Pressure

Hormones

Body temperature

Brainstem

Midbrain

Pons

Midbrain

Contains the tectal plate

• visual reflex

• auditory reflex

  → wasp

Pons

Rounded bulge that regulates breathing

Medulla Oblongata

Cardiac Center

Vasomotor Center

Respiratory Center

Reflex Center

Cardiac Center

Regulates heart rate

Vasomotor Center

Regulates blood vessel diameter

Respiratory Center

Regulates breathing

Reflex Center

Regulates swallowing, coughing

Reticular Formation

Sits in the midbrain and medulla

• Consciousness & alertness raises us from sleep

Cerebellum

Center for coordination & posture

Limbic System

Center for emotion, motivation, memory

• forms ring around the brain stem

General Senses

Temperature, pain, touch, stretch, & pressure

Special Senses

Gustation, olfaction, vision, equilibrium, & audition

Stimuli

Changes in the external or internal environment

Receptors

Detect Stimuli

Stimulus Origin

1. Exteroceptors

2. Interceptors

3. Proprioceptors

Exteroceptors

Detect stimuli from the external environment:

→ skin: pain, touch, temperature, taste, smell

Interceptors

Detect stimuli from internal organs (viscera)

Proprioceptors

Detects limb & body movements

Modality of Stimulus

1. Chemoreceptors

2. Thermoreceptors

3. Photoreceptors

4. Mechanoreceptors

5. Baroreceptors

6. Nociceptors

7. Phantom Pain

8. Referred Pain

Chemoreceptors

Sensitive to chemical change

(smell, taste)

Thermoreceptors

Sensitive to temperature change

Photoreceptors

Sensitive to light

Mechanoreceptors

Mechanical stimuli from movement, pressure, & tension in muscles

Baroreceptors

Sensitive to pressure change within body structures