Phys Lecture 12 Nerve Cells and Neurotransmitters

Nervous system

• Rapid (milliseconds-seconds)

• Voluntary and involuntary control

• NEUROTRANSMITTERS (close to cell)

Neurotransmitters

• close cell to cell

• Exocytosis of all neurotransmitters

• All have extracellular receptors

• Excitatory and Inhibitory Neurotransmitters

Endocrine system

• Slow and long lasting (minutes-hours)

• Involuntary

• HORMONES (cells very far apart)

• Transported in blood vessels and lymph vessels

Nervous system controls

The nervous system controls a lot of the endocrine system

Both nervous and endocrine systems

are long distance signaling systems

Cell to cell chemical signaling

1) Chemical signal is released outside of cell

2) Receptor for signal is

• on the plasma membrane (extracellular)

• In the cytoplasm (intracellular)

Autocrine

Chemicals that exert effects on the SAME cells that secrete them (self signaling)

Paracrine

Chemicals released by cells that effect OTHER nearby cells (next door signaling)

Endocrine

Secretion into the blood for signaling with cells far away (far away signaling)

Exocrine

Secretion into the external environment through a duct usually in an epithelium (not signaling)

1) Sensory input

Sensory receptors (millions) detect changes inside and outside of body (stimuli)

2) Integration

Processing and interpretation of sensory input (what to do)

3) Motor output

Response caused by activation of effector organs (muscles or glands)

Central nervous system (CNS)

Brain and spinal chord

• integration and command center

Peripheral nervous system (PNS)

OUTSIDE CNS: links all the body to the CNS via spinal nerves and cranial nerves

• Sensory input

• Motor output

Neuronal signaling

Acetylcholine

neurotransmitter—a chemical messenger that nerve cells use to communicate with other cells, such as muscles, glands, or other nerves.

ATP

ATP: adenosine triphosphate) is the main energy currency of the cell. (movement, transport, and chemical reactions.)

 

Epinephrine

• Epinephrine (adrenaline): A hormone and neurotransmitter. It increases heart rate, blood pressure, and energy supply—part of the “fight or flight” response.

 

Norepinephrine

• Norepinephrine (noradrenaline): Similar but also acts more as a neurotransmitter. It increases alertness, focuses attention, and helps regulate blood pressure.

Glutamate

main excitatory neurotransmitter in the nervous system. It sends signals between nerve cells and plays a key role in learning, memory, and brain function.

GABA

gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the brain. It reduces nerve activity, helps prevent overstimulation, and promotes calmness, relaxation, and sleep.

 

Serotonin

neurotransmitter that helps regulate mood, sleep, appetite, and digestion

Peripheral Nervous System Organization

Sensory input

Collect and relay information to sensory neurons

Sensory receptors

Are commonly proteins that are ion channels or G- protein coupled receptors (transplasma membrane)

Sensory receptors include

• Mechanoreceptors – detect touch, pressure, vibration (skin, ears).

• Photoreceptors – detect light (eyes).

• Thermoreceptors – detect temperature.

• Chemoreceptors – detect chemicals (taste, smell, blood pH).

• Nociceptors – detect pain.

 

Cells of the nervous system (Glia)

• supporting cells

• 1-5:1 glia:neuron ratio

• Most glia maintain MITOTIC ability- (can form tumors)

Cells of the nervous system (Neurons)

• transmit signals

• Extreme longevity: >100 years

• Amitotic: most do not divide and are not replaced if destroyed

• High metabolic rate: requires continuous supply of O2 and glucose - (brain is 2% of body mass but uses 20% of O2)

Supporting cells (Glia) of CNS

Astrocytes: most abundant

• Help regulate composition of extracellular fluid (remove K+ and neurotransmitters) (CLEAN UP)

Microglia: macrophages:

• scavengers that phagocytize debris and remodel synapses (BODY GUARDS)

BOTH CELLS FORM BLOOD BRAIN BARRIER

Supporting cells (Glia) of CNS

Oligodendrocytes: Electrical insulation

• wrap axons in myelin sheaths around axons

Ependymal cells:

• Line cavities where cilia circulate cerebral spinal fluid (CSF) to cushion and nourish CNS (ventricles)

Supporting cells (Glia) of PNS

Schwann cells: surround and form myelin sheaths around axions (oligodendrocytes in CNS)

Satellite cells: surround neuron cell body, regulate external chemical environment (CLEAN UP)

Myelination

Lipid bilayer of plasma membrane - like electrical tape around a wire

Myelin sheath

• Protects/insulates axons

• Increases action potential conduction speed

Myelinated fibers

Axons w/ myelin sheath

Nodes of ranvier

Nerofiberal nodes (gaps on axon between myelin sheaths)

Neuronal cell body (soma)

• Cell body (soma): biosynthetic center

• Contains: nucleus (mitochondria, golgi, vesicles)

• Rough ER (Nissan bodies) most active in cell body

• neurofilaments (intermediate filaments): maintain cell shape

Multipolar neurons are the most common

Neuronal processes (input)

Dendrites Receive INPUT

• Short branching: large surface area

• Convey incoming messages to cell body

• Short distance signals= graded potentials (integration)

Neuronal processes (output)

Axon: send OUTPUT -(some do/don’t have myelin insulation)

• Vary in size: (short- one meter)

• Only one per neuron

Axon hillock: copse shaped area from which axion arises

What a nerve looks like