Nervous System Structure Biology 12

The Miracle of Mind Imagine you are on a beach. What do you feel? What do you see? Smell? You can recreate the experience of being at the beach without any external stimuli. How is this possible?

What is pain? What is pleasure? What are thoughts? We know the brain is made up of cells but how does the miracle of the mind emerge from this mass of cells? The human Nervous System is a whole that is far greater than the sum of its parts.

“...from the brain, and from the brain only, arise our pleasures, joys, laughter and jests, as well as our sorrows, pains griefs and tears. Through it, in particular, we think, see, hear... Eyes, ears, tongue, hands and feet act in accordance with the discernment of the brain.” Hippocrates

Mystery of the Mind Much of what we know about the brain is drawn from inferences. There remain many unanswered questions... This makes neuroscience so fascinating!

The NS must accomplish the following: Receive sensory messages that provide information about the external environment Organize that information and integrate it with other, already stored information in useful ways. Use the integrated information to send out messages to the muscles and glands to produce organized movements and adaptive secretions

4. Provide the basis for what we call conscious experience – the stream of perceptions, thoughts and feelings that make up our mental life!

Divisions of the Nervous System Central Nervous System Brain Spinal Cord Peripheral Nervous System Sensory (Afferent) Division Somatic Sensory Neurons Visceral Sensory Neurons Motor (Efferent) Division Autonomic Nervous System (Involuntary) Sympathetic Nervous System Parasympathetic Nervous System Somatic Nervous System (Voluntary)

Central Nervous System The brain + the spinal cord The center of integration and control

Peripheral Nervous System The nervous system outside of the brain and spinal cord Consists of: 31 Spinal nerves Carry info to and from the spinal cord 12 Cranial nerves Carry info to and from the brain

Autonomic Nervous System Can be divided into: Sympathetic Nervous System “Fight or Flight” Parasympathetic Nervous System “Rest and Digest” These 2 systems are antagonistic. Typically, we balance these 2 to keep ourselves in a state of dynamic balance - homeostasis.

ANS organs of our body, such as the heart, stomach and intestines, are regulated by the autonomic nervous system (ANS). part of the peripheral nervous system controls many organs and muscles within the body. functions in an involuntary, reflexive manner. For example, we do not notice when blood vessels change size or when our heart beats faster.

The ANS is most important in two situations: 1. In emergencies that cause stress and require us to "fight" or take "flight" (run away) 2. In non-emergencies that allow us to "rest" and "digest."

What does the ANS regulate? Muscles in the skin (around hair follicles; smooth muscle) around blood vessels (smooth muscle) in the eye (the iris; smooth muscle) in the stomach, intestines and bladder (smooth muscle) of the heart (cardiac muscle) Glands

Sympathetic Nervous System It is a nice, sunny day...you are taking a nice walk in the park. Suddenly, an angry bear appears in your path.

Do you stay and fight OR do you turn and run away? These are "Fight or Flight" responses. In these types of situations, your sympathetic nervous system is called into action - it uses energy - your blood pressure increases, your heart beats faster, and digestion slows down.

The sympathetic nervous system originates in the spinal cord The sympathetic nervous system originates in the spinal cord. Neurons lead to the "target" - either a muscle or a gland. Adrenalin is involved in the activation of this system. So…

This is why you may pee when you are surprised by a bear? This tid-bit will impress your friends!

Parasympathetic Nervous System You fight off the bear and the danger is over. This calls for "Rest and Digest" responses. Now is the time for the parasympathetic nervous to work to save energy - your blood pressure decreases, your heart beats slower, and digestion can start.

Sympathetic changes are detected by polygraphs to help determine when someone is lying! These two systems are antagonists – they are opposites of each other.

ANS fun animation http://itc.gsw.edu/faculty/gfisk/anim/autono micns.swf

The Neuron The neuron is the basic functional unit of the nervous system. Function: Send impulses to and from the CNS and PNS and the effectors (muscles/glands)

Neuron Structure

Dendrite  Fine hair-like extensions on the end of a neuron. Function: receive incoming stimuli. Cell Body or Soma  The control center of the neuron. Function: Directs impulses from the dendrites to the axon. Nucleus  Control center of the Soma. Function: Tells the soma what to do.

Nodes of Ranvier  Gaps between schwann cells. Axon Pathway for the nerve impulse (electrical message) from the soma to the opposite end of the neuron. Myelin Sheath  An insulating layer around an axon. Made up of Schwann cells. Nodes of Ranvier  Gaps between schwann cells. Function: Saltatory Conduction (Situation where speed of an impulse is greatly increased by the message ‘jumping’ the gaps in an axon).

Impulses Along a Neuron Dendrites receive the nerve impulse and carry it toward the cell body, which contains the nucleus. The axon carries the impulse from the cell body toward the synaptic knobs/terminals where it will be transferred to other neurons.

Myelinated Vs. Unmyelinated Myelinated neurons carry nerve impulses faster than unmyelinated ones because the impulse jumps from one node of Ranvier to the next, instead of traveling along the whole length of the axon. This is called saltatory conduction

3 Types of Neurons There are 3 types of neurons. Sensory Neurons  Neurons located near receptor organs (skin, eyes, ears). Function: receive incoming stimuli from the environment. Motor Neurons  Neurons located near effectors (muscles and glands) Function: Carry impules to effectors to initiate a response. Interneurons  Neurons that relay messages between other neurons such as sensory and motor neurons. (found most often in Brain and Spinal chord).

Sensory Neurons Carries impulses from receptors e.g pain receptors in skin to the CNS( brain or spinal cord)

Relay Neuron/Interneuron Carries impulses from sensory nerves to motor nerves. Responsible for integration

Motor Neuron Carries impulses from CNS to effector e.g. muscle to bring about movement or gland to bring about secretion of hormone

Nerves Nerves  Collections of neurons that are joined together by connective tissue. Responsible for transferring impulses from receptors to CNS and back to effectors. http://www.youtube.co m/watch?feature=play er_embedded&v=xRkP Nwqm0mM

Impulses from PNS to CNS Specialized receptors (light, sound, taste, touch) react to a stimulus and generate nerve impulses in the sensory neurons near them. The sensory neurons carry the impulse to the spinal cord and then to the brain where interneurons interpret the sensory information The interneurons send out impulses to motor neurons which elicit a response by an effector (muscle or gland)

Reflexes The simplest neural pathway is called a reflex arc and it does NOT involve the brain The pathway is: receptor, sensory neuron, interneuron in spinal cord, motor neuron, effector

Reflex Arcs Cont’d... The fact that the ‘decision’ is made in the spinal cord saves the time that it would take the nerve impulse to travel through the many circuits of the brain. Reflexes are often so fast they are involuntary Reflexes are important mechanisms that are important in maintaining homeostasis

Reflex Arc Animations http://msjensen. cehd. umn

http://www. sumanasinc. com/webcontent/ani mations/content/reflexarcs http://www.sumanasinc.com/webcontent/ani mations/content/reflexarcs.html

Structure of a Spinal Nerve Label the handout placing the components of the reflex arc in the spinal nerve.