BIO 225

Central nervous system (CNS)

Brain and spinal cord

Integration and command center

Peripheral nervous system (PNS)

the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.

Interneuron

A nerve cell that relays messages between nerve cells, especially in the brain and spinal cord.

*unmyelinated (slow messages)*

Afferent neuron

nerve cell that sends messages to brain or spinal cord from other parts of the body; also called sensory neurons

Motor neuron

a neuron that sends an impulse to a muscle or gland, causing the muscle or gland to react

Motor division

Transmits impulses from the CNS to effector organs (muscles or glands)

Autonomic division

Controls involuntary movement of the heart, glands, lungs, and other organs

- sympathetic and parasympathetic

- Smooth muscle, cardiac muscle, exocrine glands, some endocrine glands

Exocrine glands

Glands that secrete substances outward through a duct

- Salivary, sweat, etc.

Endocrine glands

Glands of the endocrine system that release hormones into the bloodstream

- gonads, adrenal, etc.

Sympathetic nervous system

- Fight or flight

- response to danger or stress

- Activates to speed up heart rate to deliver more O2

Parasympathetic nervous system

- Rest and digest

- Relaxes body after stress

- slows heart, breathing, promotes digestion

Brain

- "higher" functions

- complex task initiation

- perception

- emotions

Spinal cord

Nerves that run up and down the length of the back and transmit most messages between the body and brain

- reflexes

What is the vertebrate CNS protected by?

Meninges and cerebrospinal fluid

Meninges

three layers of connective tissue in which the brain and spinal cord are wrapped

Cerebrospinal fluid

Fluid in the space between the meninges that acts as a shock absorber that protects the central nervous system.

Dura mater

thick, outermost layer of the meninges surrounding and protecting the brain and spinal cord

Arachnoid mater

weblike middle layer of the three meninges

- no blood. vessels (nerves)

- Criss cross fibers while creating a passageway

Pia mater

the delicate innermost membrane enveloping the brain and spinal cord

- many blood vessels pass to supply brain tissue with blood

How is the CNS isolated from the circulatory system?

Blood-brain barrier

Blood-brain barrier

Blood vessels (capillaries) that selectively let certain substances enter the brain tissue and keep other substances out

- Structural and functional roadblock to microorganisms that maybe circulating the bloodstream

Blood brain barrier selective permeability

- No pinocytosis

- Substances move via dissolving/protein exchanger/channel/pump

- Small, lipid-soluble molecules directly cross

More permeable in hormone-associated areas

- Allows secreted molecules to leave brain and enter circulatory system

Blood brain barrier tight junctions

- Tight junctions between endothelial cells line brain capillaries

- Prevents materials from leaking out of blood stream into CNS

Glial cells

cells in the nervous system that support, nourish, and protect neurons

Oligodendrocytes

Form myelin sheath in CNS

Dorsal

toward the back

DAB (dorsal, afferent, back)

Ventral

Toward the belly

Gray matter

Brain and spinal cord tissue that appears gray with the naked eye; consists mainly of neuronal cell bodies (nuclei) and LACKS myelinated axons.

White matter

Whitish nervous tissue of the CNS consisting of neurons and their myelin sheaths.

White and gray matter switch in brain and spinal cord

Gray on outside and white on inside in BRAIN

White on outside and gray on inside in SPINAL CORD

BOG (brain, outside, gray)

Sulci (sulcus)

shallow grooves

Gyri (gyrus)

Large folds of tissue covering the surface of the cerebrum

- ridges of cortex

Sulci and gyri increase surface area

Peripheral neurons

outside CNS found within neurilemma which allows regeneration

Axons of peripheral neurons are bundle into nerves

Nuclei

clusters of cell bodies in the CNS

Ganglia

clusters of cell bodies in the PNS

Fascicle

Bundle

Perineurium

surrounds each fascicle

Endoneurium

surrounds each nerve fiber

Tract (nervous system)

a bundle of axons in the central nervous system

Simple reflex arc

Sensory cells carry input from the receptor (afferent impulses) to a central interneuron, which makes contact with a motor neuron.

Sensory - motor

What is the most common type of reflex arc?

Sensory - association - motor

A withdrawal reflex involves a sensory neuron, interneuron, and motor neuron

Simple reflex arcs involve only two neurons

Sensory neuron, effector neuron

Divergent - Reflex arc

One input has various responses

Convergent - Reflex arc

multiple receptors cause same effect (analogous to polymodal)

Ipsilateral

same side

Contralateral

opposite side

Contralateral innervation

one side of the brain controls the opposite side of the body

Ascending tract

Sensory/afferent information sent from PNS receptors to CNS - sent as action potentials up spinal cord to muscles in white matter - TOWARD brain

Descending tract

Motor/efferent instructions from CNS to effector organs - sent as action potentials down spinal cord to muscles in white matter - FROM brain

Ascending and descending tracts work parallel to one another

Touch is contralateral

Hearing is contralateral and ipsilateral

Left side of brain innervates right coclea

Vision is ipsilateral

Hindbrain

- Upper spinal cord, brain stem, cerebellum

- Heart rate, respiration, sleep

Medulla oblongata

Part of the brainstem that controls vital life-sustaining functions such as heartbeat, breathing, blood pressure, and digestion.

- descending motor tract, ascending sensory, origin of cranial nerves

Pons

Regulates breath-holding, integrates among areas

- unconscious processes

- contains junction points for nerves that control muscles and carry information from sensations in head and face

Cerebellum

Maintains body posture, coordinates locomotion, integrates information from proprioceptors

Midbrain

Tectum, tegmentum

- Vision, hearing, motor control, arousal, sleep/wake, temperature regulation

Tectum (optic lobes)

processes visual, auditory, and touch information

Tegmentum

Reflex responses to visual, auditory, and touch information

Forebrain

- Controls "higher" processes