controlling your body

Nervous and Endocrine Two major components: Central Nervous System (CNS) Peripheral Nervous System (PNS) Composed of specialized cells called neurons Carry electrical impulses (not like electricity) Neurons are unlike any other cell in your body Several distinct parts: dendrites, cell body, axon, myelin sheath, nodes of Ravnier Can be very long: single axon up to a meter Bundle of neurons is a nerve…longest in the human body is the sciatic (lower back to feet)

Nervous and Endocrine Impulse (action potential) always travels from cell body to axon terminal Myelin sheath is made of Schwann cells Neurons communicate with each other from one synaptic terminal to a dendrite of another cell This arrangement can be varied (1:1, 2+:1, 1:2+)

Nervous and Endocrine Central Nervous System Brain and Spinal Column These structures receive all signals from your 5 senses If a response is needed, sent back via motor response Sensory neurons brings messages to CNS, motor neurons carry responses to muscles Peripheral Nervous System Sensory and motor neurons Nerve (multiple neurons) may be myelinated (insulated), speeding up signaling Two types of peripheral nerves: Cranial & Spinal 31 pairs of spinal nerves, mixed type (sensory/motor), come directly from spinal column 12 pairs of cranial nerves, from brainstem, (optic nerves)

Nervous and Endocrine Nerve impulses are all controlled by stimulus & response If a sensory receptor receives an electrical impulse it is ultimately sent to your brain (via an action potential) Relay neurons actually deliver the impulse to the appropriate area in the brain Brain returns a signal using relay neurons and eventually through spinal column and to an appropriate peripheral nerve Muscle will receive a chemical signal from neuron’s motor end plate, telling it to do something

Nervous and Endocrine The sequence of nerve impulses is the same regardless of the source of the stimulus Make sure you know the Batman sequence… Relay neuron

Nervous and Endocrine So what exactly is an action potential and how does it work?

Nervous and Endocrine The action potential travels much more quickly in myelinated axons The myelin sheath does not allow ions to cross the neuron membrane, so the action potentials jump from node to node This is called saltatory conduction (saltar = to jump) In non-myelinated axons the speed of the impulse is much slower The gated channels seen in the previous slide are only found at the nodes of Ravnier of myelinated axons

Nervous and Endocrine When a nerve impulse reaches the axon terminal it must transmit the signal to the effector cells or the dendrites of another neuron Small gap called a synapse…transfer of the neurotransmitters to the receiving cells is called synaptic transmission

Nervous and Endocrine Endocrine system is responsible for maintaining homeostasis It also produces and secretes hormones from glands that are usually far away from the cells which are affected by the hormone Homeostasis is the maintenance of certain body features within a specific set of limits Blood pH CO2 concentration Blood glucose concentration Body temp Water balance within tissues

Nervous and Endocrine Most homeostatic control is done through negative feedback mechanism 1 HYPOTHALMUS: sweating arteriole dilation 2 STRESS: raises body temp 3 STRESS: cold 4 HYPOTHALMUS: shivering arteriole constriction

Nervous and Endocrine Another negative feedback system in your body regulates blood glucose levels Diabetes is a disease that prevents you from being able to maintain proper glucose levels Two types of diabetes: Type I—pancreatic β cells do not produce enough insulin because they are attacked by own immune cells Type II—because of age/weight/ethnicity cells become insulin resistant, eventually insulin production can decrease

Nervous and Endocrine