Neuroscience: Nervous System Structure, Function, and Cell Types

Nervous system

Faster, more specific, directs muscular activities

Endocrine system

Slower, more general, directs metabolic activities

Chemical messengers

Both systems communicate with the rest of the body to coordinate their functions

Neurons

Basic unit of structure and function of the nervous system; capable of receiving, processing, and sending out commands via nerve impulse

Motor neurons

Neurons that carry nerve impulses away from the CNS to muscles and glands

Sensory neurons

Carry nerve impulses from sensory receptors towards the CNS

Interneurons

Connect sensory and motor neurons (only in the brain and spinal cord)

Neuron reproduction

Only occurs in the hippocampus

Neuroglia

More numerous, function in supporting neurons; do not generate or conduct nerve impulses

Astrocytes

Attach blood vessels to neurons so they can get nutrients better

Microglial cells

Protection of the brain and spinal cord from disease by phagocytosis of microbes and debris

Oligodendrocytes

Myelinate neuron axons and dendrites in the brain

Schwann cells

Myelinate neuron axons and dendrites in nerves

Myelination

Speeds up the rate at which the nerve impulse moves down the axon or dendrite

Cell body

Contains nucleus, cytoplasm, and organelles; variable in shape

Dendrites

Carries nerve impulses towards a cell body from a sensory receptor, or carries an excitatory message from an axon of another neuron to its cell body

Axon

Carries nerve impulses away from the cell body

Nerve fibers

Dendrites of sensory neurons and axons of motor neurons existing within nerves

Tracts

Bundles of axons of interneurons within the spinal cord or brain

Nucleus (CNS)

Groups of neuronal cell bodies in the central nervous system

Ganglion (PNS)

Groups of neuronal cell bodies in the peripheral nervous system

Multipolar

Many processes sticking off of a cell body

Bipolar

Two processes sticking off of a cell body

Unipolar

One process sticking off on a cell body (process divides into one dendrite and one axon)

Nerve impulse

Movement of sodium ions into a portion of an axon, and subsequent movement of potassium ions out of the same portion of the axon; followed by return of ions to original locations by sodium potassium pump

Depolarization

Movement of sodium ions into the axon

Repolarization

Movement of potassium ions out of the axon

At rest

The inside of the axon is negative compared to the outside

After depolarization

The inside of the axon becomes positive compared to the outside

After repolarization

The inside of the axon becomes negative again

What is myelination?

The process of covering axons with a white fatty layer called the myelin sheath.

What is the difference between white matter and gray matter?

White matter consists of myelinated axons and dendrites, while gray matter consists of unmyelinated axons, dendrites, and cell bodies.

How does myelination affect nerve impulse transmission?

Myelination speeds up transmission because depolarization and repolarization occur only at the Nodes of Ranvier.

What is saltatory conduction?

The process where a nerve impulse 'jumps' from node to node along a myelinated axon.

What role do Schwann cells play in the peripheral nervous system?

Schwann cells can reconnect nerve fibers and restore function when nerves are cut.

What is the function of oligodendrocytes in the central nervous system?

Oligodendrocytes cannot rejoin nerve fibers when cut, leading to permanent paralysis.

What is a synapse?

The space between the axon of one neuron and the dendrite of another neuron.

What happens when a nerve impulse reaches the end of an axon?

Calcium enters the axon, causing synaptic vesicles to fuse with the membrane and release neurotransmitters into the synapse.

What is an excitatory neurotransmitter?

A neurotransmitter that stimulates dendrites of another neuron, initiating a nerve impulse in the proximal axon. Examples include serotonin and norepinephrine.

What is an inhibitory neurotransmitter?

A neurotransmitter that prevents stimulation of dendrites, resulting in no nerve impulse. Examples include GABA and glycine.

How does acetylcholine function differently in skeletal vs. cardiac muscle cells?

Acetylcholine is excitatory with skeletal muscle cells but inhibitory with cardiac muscle cells.

What are the components of the central nervous system?

The brain and spinal cord.

What is the peripheral nervous system?

All nervous tissue outside of the central nervous system.

What is the somatic nervous system responsible for?

Conveying information from the CNS to skeletal muscles (voluntary) and sensory information from receptors to the CNS.

What does the autonomic nervous system control?

Involuntary functions, conveying information from the CNS to smooth muscle, cardiac muscle, and glands.

What is the enteric nervous system?

A system of neurons in the GI tract that operates somewhat independently of the ANS and CNS.

What are the two divisions of the autonomic nervous system?

The parasympathetic division, which stimulates organs for relaxation, and the sympathetic division, which stimulates organs during stress.

What are the three layers of the meninges?

Dura mater (outer), arachnoid mater (middle), and pia mater (inner).

What is the function of the subarachnoid space?

It is located between the arachnoid and pia mater and is filled with cerebrospinal fluid.

What is the structure of the spinal cord?

It begins at the foramen magnum, ends at the lumbar vertebrae, and is covered by the same three meninges as the brain.

What are the cervical and lumbar enlargements?

Swelling of the spinal cord that contains numerous cell bodies of motor neurons going to the upper and lower extremities.

What is the conus medullaris?

The end of the spinal cord.

What is the cauda equina?

A bundle of spinal nerves that descend from the conus medullaris into the lumbar, sacral, and coccygeal regions.

What is the function of ascending and descending tracts in the spinal cord?

Ascending tracts carry sensory information to the brain, while descending tracts carry motor nerve impulses from the brain to the spinal cord.

Endoneurium

Loose connective tissue surrounding individual axons and dendrites.

Perineurium

Connective tissue surrounding bundles of axons and dendrites called fascicles.

Epineurium

Connective tissue surrounding all the fascicles.

Sensory nerve

Collection of only sensory neuron dendrites.

Motor nerve

Collection of only motor neuron axons.

Mixed nerve

Collection of sensory and motor neurons.

Cranial nerve I

Olfactory, responsible for smell.

Cranial nerve II

Optic, responsible for vision.

Cranial nerve III

Oculomotor, responsible for motor eyeball movement.

Cranial nerve IV

Trochlear, responsible for motor eyeball movement.

Cranial nerve V

Trigeminal, responsible for sensation from head and face, maxillary, and chewing.

Cranial nerve VI

Abducens, responsible for motor eyeball movement.

Cranial nerve VII

Facial nerve, responsible for facial expression, taste, and secretion.

Cranial nerve VIII

Vestibulocochlear, responsible for balance and hearing.

Cranial nerve IX

Glossopharyngeal nerve, responsible for swallowing and speech.

Cranial nerve X

Vagus, stimulates organs, sensation, and taste.

Cranial nerve XI

Accessory, responsible for movement of head and shoulders.

Cranial nerve XII

Hypoglossal, responsible for speech and swallowing.

Spinal nerves

8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.

Posterior (dorsal) root

Contains only axons of sensory neurons.

Anterior (ventral) root

Contains only axons of motor neurons.

Cervical plexus

C1-C5, includes phrenic nerve.

Brachial plexus

C5-C8 and T1, includes median and ulnar nerves.

Lumbar plexus

L1-L4, includes femoral nerve.

Sacral plexus

L4-L5, S1-S4, includes sciatic nerve.

Coccygeal plexus

S4-S5, includes coccygeal nerve.

Thoracic and lumbar nerves

Contain sympathetic neurons.

Cranial and sacral nerves

Contain parasympathetic neurons.

Blood brain barrier

Brain capillaries have especially small openings in their walls to prevent the passage of certain substances from the blood into the brain tissue.

Cerebrum

Largest division of the brain; highly convoluted, and composed of 2 cerebral hemispheres; contains 2 lateral ventricles and is divided into lobes.

Corpus callosum

Connects hemispheres and allows communication.

Fornix

Part of the limbic system which is responsible for our emotions and memory.

Frontal lobe

Initiates voluntary skeletal muscle contraction, involved in conscious thought.

Broca's area

For planning and producing speech, in the left frontal lobe.

Parietal lobe

Interprets sensory information from the skin, and taste.

Wernicke's area

Recognizes spoken and written words.

Temporal lobe

Hearing and smelling, memory, and emotions.

Hippocampus

Site of memory.

Amygdala

Site of emotions.

Limbic system

Hippocampus and amygdala.

Occipital lobe

Perception of vision.

Basal ganglia

Regulate initiation and termination of movements by skeletal muscles, controls subconscious contractions of skeletal muscles.

Cerebral dominance

Left hemisphere controls and responds to right side of body and vice versa.

Diencephalon

Consists of thalamus, third ventricle, hypothalamus, and pineal gland.

Thalamus

Receives nerve impulses from sensory receptors and channels them to appropriate lobes of cerebrum for interpretation.

Third ventricle

Space surrounding thalamus, connected to lateral ventricles and contains CSF.