1. Biology – Premed Windsor University School of Medicine
Premed I Biology
May2015

2. Pre Med – Biology Chapter 13 The Nervous System
There is more to lectures than the power point slides!
Engage your mind

3. KEYWORDS
Gland, Hormone, Impulse, Nervous system, Effector, Stimulus, Receptor, Neuron, Synapse

4. Nervous System
Central Nervous System
Peripheral Nervous System

6. Parts of the nervous system
The nervous system is made up of three main parts;
The brain (CNS)
The spinal cord (CNS)
Nerve fibres (PNS)
It detects stimuli such as light, sounds, temperature, pressure, pain and co-ordinates the bodies response.

7. EFFECTORS
An effector is any part of the body that produces the response.
Here are some examples of Effectors:
a muscle contracting to move the arm
a muscle squeezing saliva from the salivary gland
a gland releasing a hormone into the blood

8. CNS Brain contains approximately 100 billion neurons (nerve cells)
Function of the brain is to process information arriving from other areas of the central nervous system and the peripheral nervous system via the spinal cord.

9. CNS
Function of the spinal cord is to relay messages from the brain to the peripheral nerves and from peripheral nerves to the brain
Spinal cord also controls reflex arcs or involuntary responses that bypass the brain

10. PNS
The peripheral nervous system is made up of the nerves and ganglia (groups of cell bodies of neuron) that are found outside of the CNS
Sensory neurons transmit impulses from the PNS to the CNS and motor neurons transmit impulses from the CNS to the PNS
Peripheral nerves that communicate directly with the brain are called cranial nerves (12 pairs - connect sensory receptors in nose, eyes, ears, tongue, etc.)
Peripheral nerves that communicate with the brain via the spinal cord are called spinal nerves (31 pair - muscles of the body and various glands and organs)

11. Parts of the nervous system
For example;
If you smell something burning…
Your nose (receptor) detects the stimulus (smell)
Nerve fibres send the message to the brain
Your brain then sends a message to move your body away or to put out the fire!
SIMPLE RIGHT!

12. Lets look at some bits more closely RECEPTORS
Receptors are sensors on the body that detect stimuli
They convert stimuli into electrical signals (messages) called impulses.
Eyes pick up
light waves
through the
retina
Can you think
of any receptors?
Nose picks up
chemical signals
through the
nostrils
Ear picks up
sound waves
through the
eardrum

13. NERVE FIBRES
Nerve fibres are bundles of nerve cells (neurons) that pass on electrical signals (impulses) to the brain.
From the brain, nerve fibres send impulses to effectors (muscles).

14. NEURONS Brain is made of 100 billion neurons
Basic functional unit of nervous system
Neurons are nerve cells that transfer information within the body
Each neuron has a vast number of “connections” (synapses) with other neurons
Transmit electrochemical signals along the long length of communication with other neurons

15. NEURONS There are three types of neurons:
Sensory neuron – Transmit information about external stimuli
(carries impulses from the receptors to the spinal cord following stimulation)
E.g. Respond to pressure, hot, cold, light, mechanical vibration, etc or internal stimuli such as blood pressure, muscle tension
Interneuron (Relay Neuron) – Located in CNS
(Analyze and interpret the sensory information)Receives messages from other neurons by dendrites. Relays message to motor neuron through axons
Motor Neuron – Receives signals from interneuron at dendrite, relays message to cell body in CNS. Impulse then travels to effector (muscle or gland activity)
eg. Motor neurons transmit signals to muscle cells causing contraction

16. Neurons that carry out integration (interneurons) are organized in a Central Nervous System (CNS)
Neurons that carry information into and out of the CNS are the Peripheral Nervous System (PNS)
When bundled together, Axons of neurons form the NERVES

19. Sensory neurons have long dendrites and short axons
Motor neurons have short dendrites and long axons.

21. NERVOUS SYSTEM CNS PNS SNS ANS Parasympathetic Sympathetic
Nervous system releases electrical impulses that are quick but the effects are short lived and it involves the CNS (either just spinal cord or both spinal cord and brain) messages are carried by neurons
SNS
ANS
Parasympathetic
Sympathetic
Endocrine system releases chemical signals that are slow to react but the effects are long lasting. This does not involve the CNS. Messages are carried by the blood.

22. CONTROL SYSTEMS There are two main control systems in your body.
Nervous system – which has two main sections
Central or CNS that is made up of the spinal cord and brain and functions to coordinate all actions of the body
Peripheral or PNS that is made up of the bodies nerves and functions to connect the CNS to the rest of the body through neurons. PNS is further divided into

23. 2. Peripheral Nervous System
Somatic or SNS which is associated with the voluntary control of body movements and is made up of all neurons, sense organs, skin, skeletal muscles
Autonomic or ANS which is associated with the involuntary control of body movements such as reflex and controls such things as heart rate, body temperature, digestion etc. The ANS is further divided into
Parasympathetic nervous system works in actions that do not require a fast response (rest and digest response)
Sympathetic nervous system works in actions that do require a fast response (fight or fight response)

24. Somatic Nervous System
Somatic nervous system describes peripheral nerves that receive and send signals to skeletal muscle, skin, and tendons
Sensory receptors in skin, muscle and tendons send information to the CNS about body position and environmental conditions
CNS relays signals to motor neurons that control the contraction of skeletal muscle and the movement of the body
Somatic nerves control voluntary movements of the body such as walking, jumping, writing, typing, etc

25. Autonomic Nervous System
Autonomic nervous system controls involuntary responses to stimuli by the body
Autonomic nerves serve cardiac muscle, smooth muscle, glands, and all of the internal organs
ANS acts on these various effectors to maintain homeostasis within the body
Parasympathetic branch - acetylcholine neurotransmitter
Respond to stress through sympathetic branch - norepinephrine neurotransmitter

26. Endocrine system – which is a system of glands that release a number of signalling chemicals known as hormones.

27. Neuron

28. Neurons have numerous long processes and transmit nerve impulse
Neuron has a large Cell body (soma) with two or more thin protoplasmic processes extending from it
One of the processes called the “AXON”, long and conducts nerve impulses away from the cell body
Second process conduct nerve impulses towards the cell body and are called “DENDRITES”

30. Neurons are of 3 types based on the number of nerve processes:
1. Unipolar Neurons --- Only one axon, a single process leaves the cell body
2. Bipolar Neurons --- Two processes leave the cell body: an axon and a dendritic branch
3. Multipolar Neurons --- Many processes arise from cell body

32. A neuron may have many Dendrites (extensions) that receive signals from other neurons and transmit the impulse to the cell body
Cell bodies contain cell organelles, including the nucleus, and carry out normal cell functions
Axons receive signals from the cell body and transmit the impulse away from the cell body

33. Glia or Glial cells – Supporting cells that nourish and insulate the axons of neurons

34. Extended axon or dendrite of a neuron is called a Nerve fiber
Nerve fibers are of two types:
Covered by lipid-rich insulating layer called “Myelin Sheath” or Myelinated
Not covered by myelin sheath, called “Non-myelinated”

35. Myelin sheaths (neuron wraps) are formed by Schwann Cells in the PNS (What forms myelin sheath in CNS??)
Schwann cells form multiple layers of membrane around the neuron and insulate it
In between the areas of myelin sheath, Nodes of Ranvier or bare patches exist
Nerve impulse or action potential will jump form node to node greatly increasing the speed of nerve transmission.
This node to node transmission, called saltatory conduction, can produce transmission speeds of up to 200 meters per second and explains the speed at which we can react to potentially harmful stimuli.

37. Action Potential

38. The dendrites and axons of a neuron are cell membrane, called axomembrane, that are filled with cytoplasmic fluid called axoplasm
Electrochemical signal or impulse that allows neurons to communicate travels along the axomembrane.

39. When the dendrite of a neuron receives sufficient excitatory stimulation, called threshold, an action potential results
Action potential is an "all or none response“
If stimulation exceeds the threshold, an impulse will be generated
Sub-threshold stimulation will not elicit an action potential
The stimulation that initiates an action potential usually will be generated by sensory receptors for sensory neurons and at a synapse for interneurons and motor neurons.

41. Action Potential Resting potential:
The axoplasm is kept negative relative to the outside of the neuron as 3 sodium ions are pumped out for every 2 potassium ions that are pumped in
Action Potential:
When the dendrite of a neuron receives stimulation exceeding threshold, an action potential is generated in the axomembrane of the neuron and quickly moves along the dendrite to the cell body and axon
An action potential is produced by the action of gated channel proteins embedded in the axomembrane. There are gated protein channels for both sodium ions and potassium ions.

42. Action potential has three phases--
1.Depolarization (facilitated diffusion of sodium ions)
Sodium gated channel proteins open and sodium ions rush from the outside of the axomembrane to the inside. This changes the polarity across the neuron from -65mV (resting potential) to +40mV
2.Repolarization (facilitated diffusion of potassium ions)
Potassium gated channels open and potassium ions rush to the outside of the axomembrane. This makes the outside of the membrane positively charged relative to the inside once again. The potential across the membrane returns from +40mV back to -65mV.
3. Recovery/Refractory Period (active transport of sodium and potassium ions) The sodium-potassium pump is busy re-establishing the resting potential by pumping sodium ions out and potassium ions back in through the axomembrane.

44. The Synapse

45. SYNAPSES
Where two neurons meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neuron releases the chemical into the gap. The chemical diffuses across the gap and makes the next neuron transmit an electrical signal. “The communication between neurons is chemical in nature”

47. A synapse is composed of a presynaptic membrane on the axon bulb of the first neuron and a postsynaptic membrane on the dendrite or cell body of the second neuron
A very small gap, called the synaptic cleft, lies between the presynaptic and postsynaptic membranes.

48. What is a synapse?
A synapse is a junction between two neurons across which electrical signals pass. The human body contains up to 500 trillion synapses.
presynaptic cell
postsynaptic cell

49. The release of neurotransmitters
When a nerve impulse arrives at the end of one neuron it triggers the release of neurotransmitter molecules from synaptic vesicles.
synaptic vesicle
neurotransmitter molecules

50. Continuing the impulse
The neurotransmitters diffuse across the synaptic cleft and bind with receptors on the next neurone, triggering another impulse.
synaptic cleft
nerve impulse
receptor

51. Neurotransmitters can cause excitation or inhibition at the postsynaptic membrane
E.g. Acetylcholine and Norepinephrine
A single neuron will have many dendrites and many synapses with other neurons
Many excitatory signals will depolarize the neuron and cause an action potential, while inhibitory signals super polarize the neuron and prevent an impulse being generated

52. Command & Control Center

53. Pairs of Cranial nerves, spinal nerves and ganglia make up most of the peripheral nervous system

54. Gray Matter – Made up of neuron cell bodies
White Matter – Made of bundled axons

56. REFLEX ARC
When your body needs to react to something very quickly (to protect itself) it uses a reflex arc (spinal reflex).
Instead of sending impulses from the receptor
Spinal cord brain spinal cord effector
It sends impulses from the receptor
spinal cord effector…Yup it bypasses the brain!

57. Reflexes = Body’s automatic responses to certain stimuli
Reflex protects the body by providing a rapid, involuntary response to a particular stimuli

59. Peripheral Nervous System
Transmits information to and from the CNS
Afferent – Sensory information reaches CNS
Efferent – Once processed within CNS, instruction travels to muscles and glands.
PNS has 2 Efferent components:
1. Motor system – Carry signals to skeletal system ( Voluntary and Involuntary)
2. Autonomic Nervous System (Involuntary)

60. 3 divisions of Autonomic Nervous System:
Sympathetic (“Fight or Flight Response”)
Parasympathetic ( “Rest & Digest”)
Enteric – Digestive tract
Sympathetic – heart beats faster, digestion is slowed or inhibited, adrenal medulla secretes epinephrine (adrenaline), glucose production
Parasympathetic – heart rate decreases, digestion increases, glycogen production

63. ANSWERS
Electrical impulses along neurons, chemical (neurotransmitters) across the synapse.
The microscopic gap between two neurones.
By chemicals called neurotransmitters.
To pass the impulse onto the correct motor neurone.
Glands or muscle that produce the
effect or make a response.

64. The sequence of a reflex arc
Teacher notes
This ordering activity could be used as a plenary or revision exercise on reflex arcs. Mini-whiteboards could be used to make this a whole-class exercise.

65. REFLEX ACTION In bright light In dim light
Radial muscles of the iris relax.
Circular muscles of the iris contract.
Less light enters the eye through the contracted pupil.
Radial muscles of the iris contract.
Circular muscles of the iris relax.
More light enters the eye through the dilated pupil.
The way the iris in our eye adjusts the size of the pupil in response to bright or dim light is also a reflex action.

66. The iris reflex

67. Inside the eye cornea protects eye surface and focuses light rays
hold lens in place
suspensory ligaments
retina
senses light
lens
focuses light on retina
iris
regulates amount of light entering eye
ciliary muscles
change shape of the lens
optic nerve
transmits impulses to the brain

68. BRAIN

73. The brain is divided into a left and a right hemisphere
Each hemisphere is further divided into four lobes
The left hemisphere of the brain controls the right side of the body and the right hemisphere controls the left side of the body
The two hemispheres are connected by the corpus callosum which allows communication between the two sides of the brain

74. Cerebrum
The cerebrum is the largest part of the human brain and gives us consciousness and the ability to think, wonder, ponder, etc.
It is highly convoluted in structure
The cerebrum is responsible for receiving sensory signals (ex. touch) and controlling voluntary responses by the body such as movement

75. Thalamus The thalamus is called the "gatekeeper" for the cerebrum
All information received by the cerebrum is routed through the thalamus (except smell).
The thalamus also plays a role in the reticular activating system (RAS) that makes the cerebrum aware of important stimuli (perhaps awakening you from sleep) and filters out unimportant stimuli (background noise).

76. Hypothalamus The hypothalamus lies below the thalamus
It functions in maintaining homeostasis in the body
Some of the bodily functions controlled by the hypothalamus are sleep, hunger and thirst, water balance, blood pressure, and body temperature (thermostat). The mechanism by which it controls these functions often involves hormones released from the pituitary gland that have effects on target organs in the body such as the thyroid gland, adrenal glands, and kidneys

77. Medulla Oblongata
The medulla oblongata is located in the brain stem at the base of the skull
It has neurons that communicate with both the brain and the spinal cord.
The medulla oblongata controls involuntary functions vital to life and is the site of the respiratory (breathing) and cardiac (heartbeat) control centers mentioned earlier in the course
Other reflexes controlled by the medulla oblongata include; vomiting, coughing, sneezing, hiccupping, and swallowing.

78. Cerebellum
The cerebellum lies behind the brain stem. It is responsible for muscular coordination and balance
Receives information about positions of the joints and lengths of muscles
Hand-eye coordination

79. Pituitary Gland The pituitary gland is made up of the anterior pituitary and posterior pituitary (one lies in front of the other)

80. REFLEX ACTION

81. NERVE PATHWAY… Have a go at completing this worksheet

82. NERVE PATHWAY… answers
SENSE ORGAN/ RECEPTOR
Senses stimuli from our surroundings.
SENSORY NEURON
Takes impulses from the sense organ to the relay neuron.
SPINAL CORD
Where the relay neurones are found.
RELAY NEURON
Takes impulses to the brain and from the brain.
EFFECTOR
The muscle that receives the impulse from motor neuron.
BRAIN
Receives impulses from the spinal cord and sends out new impulses.
MOTOR NEURON
Takes impulses from the relay neuron to the effector.

83. Summary/Terms (1/2)
accommodation – The reflex reaction that keeps the lens the right shape to focus light on the retina.
CNS – The central nervous system, consisting of the brain and spinal cord.
iris – The part of the eye that limits the amount of light entering the eye.
lens – The part of the eye that focuses light on the retina.
motor neuron – A neuron that carries electrical impulses from the CNS to muscles and glands.
neuron – A specialized cell that carries electrical impulses.

84. Summary/Terms (2/2)
neurotransmitter – A chemical that diffuses across synapses to continue an impulse in a connecting neurone.
reaction time – The time taken to respond to a stimulus.
reflex – A fast, automatic protective response.
retina – The part of the eye that contains light receptors.
sensory neuron – A neuron that carries electrical impulses from sense organs to the CNS.
synapse – The gap between two connecting neurons.

85. STARTER
ENDOCRINE SYSTEM
Name the hormones –write down the names of the hormones secreted by the glands. Name the hormones – Have you thought of any others? Time: 10 minutes Working Groups: Your choice of 1, 2 or 3

86. STARTER answers
Pituitary gland – FSH, LH (stimulates the release and maturity of follicles during menstruation) Thyroid gland – Thyroxine (regulates the rate of metabolism) Adrenal gland - corticosteroids and catecholamines including cortisol and adrenaline and small amounts of testosterone (regulates stress levels) Pancreas – peptides (regulates the production of shorter active digestive enzymes) Ovary – oestrogen, progesterone and small amounts of testosterone (regulates the growth of eggs and stabilises the growing foetus during pregnancy) Testis – testosterone (plays a key role in the health and well-being of the man)