The Nervous System:

a vast array of cellular

communications

Nervous SystemNervous System

The real work of your brain goes on in individual cells. An adult brain

contains about 100 billion nerve cells, or neurons, with branches that connect at more than 100 trillion

points Each nerve forms about 1000

synapses each!

Nervous System

• Central Nervous System – Brain and Spinal Cord (CNS)

• Peripheral Nervous System – Everything else (PNS)

Nervous System

• Afferent (Sensory)– Sends information to the

brain– Cell bodies in PNS– Types

• Cutaneous (pain, pressure, touch)

• Proprioceptors (measure stretch in muscles)

• Special senses (hearing, taste,sight, smell)

• Efferent (Motor)– Send info. from the

brain to make things happen

– Cell bodies in CNS– Types

• Somatic (conscious control – skeletal muscles)

• Autonomic (involuntary responses – cardiac and smooth muscle, glands)

Efferent Nervous SystemAutonomic Branch

SympatheticFight or FlightE – energetic,

exercise, excitement, embarassment

ParasympatheticRelaxingD – digestion,

defecation, diuresis

Sympathetic and Parasympathetic work opposite each other – what one does, the other does the opposite

Cells of the Nervous System

Neurons– Axons away, usually 1, long, branch at end– Dendrites – input to neuron, many, shorter

Neuroglia or Glial cells (support cells)– Can divide but can’t transmit impulses– Support, insulate, protect neurons

Support Cells of the CNS• Astrocytes – star shaped (about ½ of CNS

tissue), anchor neurons to capillaries, barrier between blood and neurons to capture toxins, pick up excess ions and neurotransmitters

• Microglia – phagocytes• Ependymal Cells – ciliated epithelium that line

the brain and spinal cord, move CSF around• Oligodendrocytes – wrap around nerve fibers

producing the myelin sheath (fat covering of nerves to increase nerve conduction speed)

Support Cells of the PNS

• Schwaan Cells – form the myelin sheath in PNS (have gaps in between sheath called Nodes of Ranvier)

• Satellite Cells – cushions nerves

• Ganglia – a bunch of cells bodies located in the PNS

Structure of a NerveStructure of a Nerve

Nerve Cell Structure

Nerves

• Irritability – transfer impulses to the nerve cell• Conductivity – transfer impulses from the nerve

cell to an organ or other nerve cell

• Reflexes – impulse goes to the spinal cord and back directly without going to the brain– Autonomic – pupils, glands– Somatic - muscles

Neuron Structure

• At the edges of the cell body are dendrites which receive information via. receptors

• There is one long axon (can be up to 3 meters) to send signals out by releasing neurotransmitters (usually proteins)

How do neurons send and receive signals?

• Axon terminals branch out and connect with dendrites of many other nerve cells (synapses)

• In a synapse, the axon and dendrite don’t touch, there is a gap

• At each axon terminal, there are vesicles containing a neurotransmitter

• Once the neurotransmitter is released, it binds to receptors on the dendrite

• The chemical signal gets transduced to an electrical signal

• Some neurotransmitters send excitatory signals (causing the neuron to send a signal to the next one) and some inhibitory

• When the excitatory signals are greater than the inhibitory ones, the signal is sent to other neurons.

How does the neurotransmitter signal get converted to an electrical signal?

• Normally, there is more Na+ outside the cell than K+ inside so the normal cell is slightly negative inside compared to the outside (called resting potential)

• The binding of the neurotransmitters opens gated channels letting the Na+ and K+ freely diffuse, erasing the charge (depolarization)

• This travels down the dendrite

of the receiving cell all the

way to its own axon terminals

• As Na+ enters the cell at the axon terminal it opens gated channels letting Ca+2 in.

• Calcium causes the vesicles to fuse with the membrane and release the neurotransmitter into the next synapse.

• The neurotransmitter binds to the receptors on the dendrites gets converted to an electrical signal and on and on

Overall Process

How does it all work together? • Brain receives all of its sensory input (sight, hearing,

taste, smell, pain, touch, pressure, proprioception, internal conditions, vestibular (balance)) by the sensory neurons releasing neurotransmitters in the brain to the correct receiving neurons. Neurons for each senses are located in different areas of the brain.

• The brain integrates this information to understand the whole picture by sending and receiving signals within the brain neurons themselves

• To respond, the brain then sends out information via neurotransmitters to: glands to secrete hormones, to skeletal muscle to make you move, to smooth muscle to make something squeeze involuntarily

Brain Structure

Brain and Brain Parts

• Cerebral Hemispheres (Cortex)• Dienchephalon

– Thalamus – relays sensory input to the cortex– Hypothalamus – endocrine and nervous tissue – major

homeostasis center - regulates temperature, hunger, thirst, water balance, emotion, pituitary

– Pituitary – endocrine gland – growth hormone, FSH, LH, TSH, etc.)

– Pineal Gland – effected by light – controls seasonal breeding

• Brain Stem – regulates blood pressure and breathing

– Midbrain – eye reflexes– Pons & Medulla Oblongata – control heart rate,

constriction of blood vessels, digestion, breathing

• Cerebellum – fine motor control, balance and coordination

Brain – Cerebral Cortex

Frontal lobe – helps control skilled Frontal lobe – helps control skilled muscle movements, mood, muscle movements, mood, planning for the future, setting goals planning for the future, setting goals and judging priorities.and judging priorities.

Occipital lobe – helps process visual information.Occipital lobe – helps process visual information.

Temporal lobe – processes hearing, memory and language functions. Temporal lobe – processes hearing, memory and language functions.

Parietal lobe – receives and processes information about temperature, Parietal lobe – receives and processes information about temperature, taste, touch, and movement coming from the rest of the body. taste, touch, and movement coming from the rest of the body. Reading and arithmetic are also processed in this region.Reading and arithmetic are also processed in this region.