Nervous Systems

1. Nervous Systems

2. The nerve cell or neuron, is the functional unit of the nervous system. It reacts using sensory cells, by sending an electrical signal along two or more neurons to reach an effector cell. • Effector cells are the cells that produce a response. • The neural response pathways are very specific. The receptor cells only respond to a specific signal. • Because of the directness and speed or neural responses, control via nerves is usually extremely rapid, short in duration and very precisely located.

3. Nervous responses require more energy than hormonal responses. Hormones are sent using the circulatory system, nervous responses are electrical signals sent down neurons, and it requires a lot of energy to restore the ion balance after a signal is sent. • Basic structure and neuron function is very similar in all groups of the animal kingdom. • In nervous systems nerve cells connect to form pathways between sensory receptors, a central brain and a responsive organ.

4. Evolution has led nerves to form the development of complex nervous systems made up of coordinating groups of nerve cells connected to path-ways of sensory (receptor) and motor (muscle or gland)nerve fibers. • More complex animals have nerve cells grouped together, forming one or more structures similar to small-brains called ganglia. Which can receive and coordinate information from sensory cells in all parts of the body to create the appropriate response.

5. Over the course of evolution animals developed to have their sensory organs in the front of their body, as it would be the first to meet the new environment. • It also lead to having a coordinating brain closer to all these sensory organs (ie a head). • In mammals coordination largely occurs in the brain and spinal cord which are known as the central nervous system. • Information is relayed to and from the CNS by neurons lying outside the spinal cord and brain called peripheral nervous system.

8. Reflex Responses • The ability to detect and quickly respond to changes in internal and external environments is essential for an animals survival. • Pain is what you feel as a result of excessive stimulation of sensory receptors in the skin. • A reflex is a action that occurs before your brain processes the information. • For example if you step on a pin, your foot will pull away before your brain even realizes you have stepped on it. • This kind of reflex protects us from further injury.

9. Stimulation of sensory receptors in the skin send a message to the spinal cord, from there the message is passed on to nerves to respond and pull away from the signal. At the same time a message is sent to the brain so you become away of the pain. • Reflexes are the simplest type of nervous response in animals and may involve as little as 2 or 3 cells. • The response is unconscious and automatic, it is not modified by information received from any other part of the body.

10. Reflexes are important as they cause a reaction often in defense of injury. Ie. Falling, the knee jerk to overstretched tendons. • If you concentrate you can often overcome some of the reflex, or the reflex entirely. The brain can overcome the unconscious reaction if you know it is coming and focus consciously to send signals and repress the reflex. • For example most people don’t pull away during an injection.

11. Reflexes are occurring all the time, especially in regards to posture. These small reflexes will take cues from your ears, eyes, joints and muscles. • Try standing on one foot. • Now try standing on one foot with your eyes closed. That shows you the importance of visual cues in posture. • Stretch receptors in tendons and muscles give the body information about the length of muscles and precise position of muscles (These are known as kinesthetic receptors).

12. A good example of these muscle and tendon reflexes in posture is when you are standing up, our body will sway slightly, and as it goes forward our calf muscles are stretched and the reflex is to contract them. This pulls your body back to a stable upright position.

13. Reflexes are also involved in some homeostatic regulations in the body such as the circulatory system. • For example the baroreceptor-heart rate reflex helps maintain blood pressure. • An increase in blood pressure increases the stretch on barorecptors in many arteries causing these receptors to increase activity. This in turn leads to a decrease in heart rate, and that decreases blood pressure.

14. Interneurons and Integration • When interneurons are added to a pathway, the possibility of coordination and integration increases. • For example most movements at joints use actions of opposing sets of muscles of flexion and extension. • Your biceps cause the flexion, and your triceps will extend your arm. However when your biceps are activated to contract, your triceps receive a signal to inhibit their flexion. This prevents the opposing muscles from flexing at the same time.

15. Most reflexes are even more complex as they need to coordinate full body movement to get away from the stimulus, for example if you step on a nail or pin, you have to shift your body weight and force to the other foot. If you simply moved the foot on the nail you would fall on your face. • Interneurons allow for coordinated responses and in the human body 97% of human neurons are interneurons.

16. The Human Nervous System • Most integration in humans occurs in the CNS (brain and spinal cord). Different regions of the brain are responsible for particular functions. • Cerebral cortex: Associated with motor activity, sensory input, speech, sight and breathing. • Hypothalamus: Receives info relating to the well-being of the body, functions in maintaining homeostasis.

17. Cerebellum: is involved in the coordination of muscle activity, including posture, balance and movement. • Brainstem: is associated with control of the heart, blood vessels and lung ventilation. • Along with coordinating information from the body to create the appropriate responses. The brain also stores information so that responses can take into account past experiences. • Pg 282

18. Peripheral Nervous System • The PNS is made up of sensory nerves (carry signals to CNS) and motor nerves (carry signal to the effector organs). • The motor component of the PNS has 2 divisions, autonomic (involuntary) and somatic (voluntary). • The voluntary or somatic system involves functions over which you have control (movement).

19. Autonomic Nervous System • The autonomic or involuntary nervous system is involved in the unconscious responses such as constriction of pupils, secretion from glands, heart rate changes. • It sends signals to heart muscle, smooth muscle (internal organs), glandular tissue and regulates the digestive, cardiovascular, endocrine, respiratory and excretory systems.

20. Autonomic Nervous System Cont’d • There are two main subdivisions of the ANS, the sympathetic and parasympathetic. They work in similar but generally opposite ways. • Sympathetic: typically increases energy use and prepares the body for action in emergency situations by increasing HR and metabolic rate. • Parasympathetic: typically enhances activities that conserve energy, such as digestion, and slowing the HR.

21. The enteric nervous system is an extensive network of cells (and reflexes) within the wall of the gut that coordinate the functions of the gut.

22. Major Sense Organs • Animals have sensory receptors to detect aspects of their environment that may affect their ability to survive and reproduce. • The type of receptors present and their sensitivity differ between animals and are related to their lifestyle. • Humans have 5 special senses: vision, hearing, taste, smell, and touch. • They are perceived through sense organs (eyes, ears, nose, tongue and skin)

23. These receptors can be classified into three main types. Photoreceptors (vision), Chemoreceptors (taste, smell, communication) or Mechanoreceptors (hearing, balance, pressure, touch). • The other receptors in the body or on the surface provide the information for the general senses such as pressure, pain, and joint position and some internal states such as BP and blood chemistry. These are known as visceral receptors or enterorecptors.

24. Vision • Visual stimulus in the form of light enters a human eye through the cornea and passes through a lens where it is focused onto the retina. • The retina contains two kinds of photoreceptors; cones and rods which contain light-sensitive pigments. • Fibres from both cones and rods lead to the optic nerve from the back of the eye and carry coded information to the brain in the form of a nerve impulse.

26. Cone cells function in the highest light intensities, and can detect colour and detail. Cones are most concentrated in the central region of the retina. • Cones provide us with our central vision which is used when a person looks straight at an object. • Rod cells detect light of low intensity and can detect movement of an object. Rods do not distinguish colour or detail, and occur at the highest concentration in the outer areas of the retina.

28. Human Taste Receptors • In humans taste receptors are located in taste buds located on the tongue. • Each taste bud is a collection of about 50 receptor cells. • Nerves from these receptors transmit impulses that carry info about the taste of a dissolved substance that enters the mouth. This info is then decoded and interpreted in the brain. • Taste receptors can detect chemical substances that are in solution in the water saliva of the mouth.

29. There are 5 basic tastes which have been identified: Sour, salt, bitter, sweet and umami. • Umami is a taste sensation produced by monosodium glutamate (MSG) and other glutamates found in fermented foods. • The traditional tongue map have been found to be wrong. All taste buds can detect all 5 tastes.

31. Human Olfactory Receptors (smell) • We smell something when vapours consisting of small lipid-soluble molecules bind to receptors. This triggers an impulse to signal the brain. • Olfactory receptors in the nose can detect substances at a concentration of 10,000 times less than that required for detection in taste receptors. • People do however vary in the smell sensitivity. There is a particularly large difference in sensing the odour of steroid-type substances, women are about 1000 times more sensitive to it.

33. The “taste” of food • The ‘taste’ of many foods is a complex sensation, as it is a combination of several sensory imputs. • They include olfactory stimuli from odour(before and while in the mouth), tactile stimuli from the texture of the food, gustatory stimuli arising from the taste of the dissolved food, and temperature stimuli. • We use a combination to get the general taste of food. And often use both the taste and smell to determine if we need to reject the food if it has gone off or spoiled.

34. Touch and Other Tactile Senses • Receptors to detect stimuli that produce the sensation of touch, pressure, temperature and pain are distributed over the entire skin surface. To stimulate a tactile receptors an object must make physical contact with the body. • Whiskers and bristles around the face of many mammals have touch receptors at their base. These acted as extensions of the body surface to increase a mammals ability to collect information.

35. congenital insensitivity to pain with anhidrosis," referred to as CIPA. • His family was shocked when Roberto started teething. He gnawed on his own tongue, lips and fingers to the point of mutilation. • Can’t sweat. • These genetic disorders affect the autonomic nervous system -- which controls blood pressure, heart rate, sweating, the sensory nerve system and the ability to feel pain and temperature.

36. For some children it's a mild degree such as breaking a leg, they'll get up and walk on the leg. They feel that something is uncomfortable but they keep on moving," she said. "For other children, the pain loss is so severe that they can injure themselves repetitively and actually mutilate themselves because they don't know when to stop. • part of this sensory disorder is difficulty "telling where they are in space."

37. Ears and Hearing • The ears of all mammals share a common structure. Three regions are commonly identified. • The outer ear consists of an external ear, made of cartilage, that leads into an ear canal. The canal ends in a delicate membrane (eardrum). The purpose of the outer ear is to gather sound waves.

38. 2. The middle ear is an air filled cavity that contains three tiny bones that are joined by elastic ligaments. Sound waves cause the eardrum to vibrate, and this vibration is then conducted across the middle of the ear by these three bones to the inner ear. The force of the vibration is magnified because it is transmitted from a relatively large area of the eardrum to a much smaller one in the inner ear. The middle ear functions to magnify sound vibrations.

39. 3. The inner ear consists of a small coiled structure, known as the cochlea, which is filled with fluid. Vibrations that reach the inner ear produce pressure waves in this fluid. The sound receptors are minute hair cells located on a membrane inside the cochlea. Information about the sound stimulus is encoded into nerve impulses and sent to the brain. The inner ear is what receives the sound stimulus.

41. The human ear also functions in maintaining balance, but we will not be discussing the structures and mechanisms of this process. • Not all mammals have an external ear, and those that do vary in size and shape.