Neural Control and the Senses

1. Neural Control and the Senses Starr, Chapter 25

2. The nervous system includes all the nervous tissue in the body plus the body�s sensory organs, such as the eyes and ears. The Nervous System

3. The Nervous System Nervous tissue is composed of two kinds of cells: Neurons - transmit nervous system messages Glial cells - support neurons and modify their signaling Neurons: Communication units of nervous systems � transmit signals Detect information about internal and external conditions Issue commands for responsive actions Neurons: Communication units of nervous systems � transmit signals Detect information about internal and external conditions Issue commands for responsive actions

4. Human Nervous System The two major divisions of the human nervous system are: Central nervous system (CNS) brain spinal cord Peripheral nervous system (PNS) nerves that thread throughout body plus sensory organs PNS � neural tissue outside the CNS plus sensory organs PNS � neural tissue outside the CNS plus sensory organs

5. Divisions of PNS Afferent division � brings sensory info to CNS Efferent division � carries action (motor) commands to bodies effectors � muscles and glands

6. Divisions of the Nervous System The nervous system has two central branches: CNS � brain and spinal cord PNS � all nervous tissue outside the brain and spinal cord, plus sensory organs Let�s look at how these two interact: Info about body and its environment comes to nervous system from its sensory receptors, for example cells in eyes which are part of PNS: Info then goes to afferent division of PNS to the brain and spinal cords. After processing this info, brain and spinal cord issue motor commands through PNS efferent division. Commands go to effectors such as skeletal muscles and glands. PNS efferent division has two systems within it: Somatic nervous system - provides voluntary control over skeletal muscles Autonomic system � provides involuntary regulation of smooth muscle, cardiac muscle, and glands sympathetic division- has stimulatory effects (Fight or flight) parasympathetic division - has relaxing effects (rest and digest)The nervous system has two central branches: CNS � brain and spinal cord PNS � all nervous tissue outside the brain and spinal cord, plus sensory organs Let�s look at how these two interact: Info about body and its environment comes to nervous system from its sensory receptors, for example cells in eyes which are part of PNS: Info then goes to afferent division of PNS to the brain and spinal cords. After processing this info, brain and spinal cord issue motor commands through PNS efferent division. Commands go to effectors such as skeletal muscles and glands. PNS efferent division has two systems within it: Somatic nervous system - provides voluntary control over skeletal muscles Autonomic system � provides involuntary regulation of smooth muscle, cardiac muscle, and glands sympathetic division- has stimulatory effects (Fight or flight) parasympathetic division - has relaxing effects (rest and digest)

7. Within PNS efferent division are two subsystems: Somatic nerves � (green) voluntary control over skeletal muscles Autonomic nerves � (red) involuntary regulation of smooth muscle, cardiac muscle, and glands Somatic (in green) � voluntary; motor function Autonomic (in red): involuntary; regulates smooth muscle, cardiac muscle, and glands; two types: Parasympathetic Sympathetic Somatic (in green) � voluntary; motor function Autonomic (in red): involuntary; regulates smooth muscle, cardiac muscle, and glands; two types: Parasympathetic Sympathetic

8. Autonomic system divided into: Sympathetic division � stimulatory effects Respond to stress or physical activity � �fight-or-flight� response Parasympathetic division � relaxing effects Sympathetic division � Respond to stress or physical activity (fight or flight response) � generally activate bodily functions Parasympathetic division � The parasympathetic division is often called the rest-and-digest system because it conserves energy and promotes digestive activities. Sympathetic division � Respond to stress or physical activity (fight or flight response) � generally activate bodily functions Parasympathetic division � The parasympathetic division is often called the rest-and-digest system because it conserves energy and promotes digestive activities.

9. Opposing Systems Most organs receive both sympathetic and parasympathetic signals Example: Sympathetic nerves signal heart to speed up; parasympathetic stimulate it to slow down Synaptic integration determines response

10. The Autonomic Nervous System

11. Types of Neurons Sensory neurons Detect and relay info Motor neurons Transmit signals from inter-neurons to effectors Inter-neurons Receive and process info Located entirely within CNS Sensory neurons � sense conditions inside and outside the body and convey info about these conditions to neurons inside the CNS Motor neurons � carry instructions from CNS to such structures as muscles or glands Interneurons � located entirely within the CNS and interconnect other neurons Sensory neurons � sense conditions inside and outside the body and convey info about these conditions to neurons inside the CNS Motor neurons � carry instructions from CNS to such structures as muscles or glands Interneurons � located entirely within the CNS and interconnect other neurons

12. Cells of the Nervous System Dendrites � receive signals (from brain and spinal cord) to effectors (such as muscles or glands) Info flows in one direction, from dendrites & cell body (input zone) to trigger zone, then along axon (conducting zone) to its endings (output zone). Glial cells produce fat-rich wrapping called myelin, can surround axons and increase speed of neural signals. Dendrites � receive signals (from brain and spinal cord) to effectors (such as muscles or glands) Info flows in one direction, from dendrites & cell body (input zone) to trigger zone, then along axon (conducting zone) to its endings (output zone). Glial cells produce fat-rich wrapping called myelin, can surround axons and increase speed of neural signals.

13. Neuroglia (glial cells) Cells that assist, support, and protect neurons Make up more than half the volume of the vertebrate nervous system A nerve is a bundle of axons in the PNS that transmits info to or front the CNS � see next slide A nerve is a bundle of axons in the PNS that transmits info to or front the CNS � see next slide

14. Nerve A bundle of axons enclosed within a connective tissue sheath

15. Nervous System Communication Understood easiest as a two-step process: Signal movement down a neuron�s axon Signal movement from this axon to second cell across structure known as synapse

16. Information Flow

17. Action Potential How nerve cell conduct signal along axon Inside neuron changes from negative to more positive - based on Na+ and K+ movement along membrane Repeats from point of stimulation to move signal along membrane Show diagram ! Show diagram !

18. Myelin Sheath

19. Chemical Synapse How nerve cells send message between cells Occurs in gap between two cells (terminal of one cell to input zone of another cell) Neurotransmitter diffuses across synaptic cleft and binds to receptors on membrane of second cell Nerve signal moves from one neuron to another (or from a neuron to a muscle or gland cell) across a synapse. Gap between cells is called synaptic cleft Nerve signal moves from one neuron to another (or from a neuron to a muscle or gland cell) across a synapse. Gap between cells is called synaptic cleft

20. Nervous System Communication

21. The Spinal Cord Gray matter (H-shaped) Mostly cell bodies of neurons (no myelin) White matter Mostly axons Sensory and motor neurons Meninges Protective coverings In cross section, the spinal cord has a darker, H-shaped central area, composed mostly of the cell bodies of neurons (gray); and a lighter peripheral area, composed mostly of axons. These two areas are the gray matter and white matter of the spinal cord, respectively. Sensory neurons � have cell bodies outside spinal cord (in dorsal root ganglia) In cross section, the spinal cord has a darker, H-shaped central area, composed mostly of the cell bodies of neurons (gray); and a lighter peripheral area, composed mostly of axons. These two areas are the gray matter and white matter of the spinal cord, respectively. Sensory neurons � have cell bodies outside spinal cord (in dorsal root ganglia)

22. Functions of Spinal Cord Expressway - channels sensory impulses between brain and peripheral nerves Communication center � receives input from sensory neurons and directs motor neurons with no input from the brain spinal impulses do not involve the brain Channels sensory impulses to the brain Communication center Receives input from sensory neurons and directs motor neurons with no input from brain. -- spinal reflexes do not involve the bring Channels sensory impulses to the brain Communication center Receives input from sensory neurons and directs motor neurons with no input from brain. -- spinal reflexes do not involve the bring

23. Reflexes Automatic movements in response to stimuli In simplest reflex arcs, sensory neurons synapse directly on motor neurons Most reflexes involve an interneuron Help us to avoid danger or preserve a physical state Help us to avoid danger or preserve a physical state

24. Reflex Arc

25. The Brain The brain contains almost 98% of the body�s neural tissue. The brain contains almost 98% of the body�s neural tissue.

26. The Human Brain There are six major regions in the adult brain: Cerebrum Thalamus and hypothalamus Midbrain Pons Cerebellum Medulla oblongata

28. Cerebrospinal Fluid Surrounds the spinal cord Fills ventricles within the brain Blood-brain barrier controls which solutes enter the cerebrospinal fluid

29. Anatomy of the Cerebrum Largest and most complex part of human brain Divided into right and left cerebral hemispheres Thin outer layer (cerebral cortex) is site of our highest thinking

30. Lobes of the Cerebrum

31. The Human Brain The brainstem is a collective term for three brain areas�the midbrain, pons, and medulla oblongata These brainstem structures are active in: Controlling involuntary bodily activities (such as breathing and digesting). Relaying information. Processing sensory information.

32. The Brain Stem

33. The Human Brain Most of the body�s sensory perceptions are channeled through the thalamus before going to the cerebral cortex. The hypothalamus is important in sensing internal conditions and in maintaining stability or homeostasis in the body, largely through its control of many of the body�s hormones.

34. Our Senses Human beings have more sensory capabilities than the famous five of vision, touch, smell, taste, and hearing Human beings have more sensory capabilities than the famous five of vision, touch, smell, taste, and hearing

35. Our Senses Each sense employs cells called sensory receptors that do two things: Respond to stimuli Transform these responses into the language of the nervous system � electrical signals that travel through action potentials Response to stimuli (such as vibration in sound) Signals from every sense except smell are routed through the brain�s thalamus and then to specific areas of the cerebral cortex. Response to stimuli (such as vibration in sound) Signals from every sense except smell are routed through the brain�s thalamus and then to specific areas of the cerebral cortex.

36. Receptors in Skin

37. Smell A special sense Olfactory receptors Receptor axons lead to olfactory lobe Our sense of smell, or olfaction, works through a set of sensory receptors whose dendrites extend into the nasal passages Odorites (molecules with identifiable smells) bind with hair-like extensions of these dendrites, resulting in nerve signal to the brain. Our sense of smell, or olfaction, works through a set of sensory receptors whose dendrites extend into the nasal passages Odorites (molecules with identifiable smells) bind with hair-like extensions of these dendrites, resulting in nerve signal to the brain.

38. Taste A special sense Chemoreceptors Five primary sensations: sweet, sour, salty, bitter, and umami Our sense of taste works through a group of taste cells, located in taste buds near the surface of the tongue, which have receptors that bind to �tastants,� or molecules of food that elicit different tastes. A given taste cell can respond through any of four (or perhaps five) chemical signaling routes that correspond to the basic tastes of sweet, sour, salty, and bitter and a possible taste of umami. Our sense of taste works through a group of taste cells, located in taste buds near the surface of the tongue, which have receptors that bind to �tastants,� or molecules of food that elicit different tastes. A given taste cell can respond through any of four (or perhaps five) chemical signaling routes that correspond to the basic tastes of sweet, sour, salty, and bitter and a possible taste of umami.

39. Our Sense of Vision Perceives visual field Lens collects light Image formed on retina Photoreceptors are rods and cones Photoreceptors are rods and cones

40. Human Eye Light first enters the eye through the cornea and then passes through the lens and various materials on its way to a layer of tissue called the retina at the back of the eye. Light is bent or refracted by the cornea and the lens in such a way that it ends up as a tiny, sharply focused image on the retina. Light signals are converted to nervous system signals by cells in the retina called photoreceptors, which come in two varieties: rods and cones. Rods function in dim light but are not sensitive to color. Cones function best in bright light but are sensitive to color. Light first enters the eye through the cornea and then passes through the lens and various materials on its way to a layer of tissue called the retina at the back of the eye. Light is bent or refracted by the cornea and the lens in such a way that it ends up as a tiny, sharply focused image on the retina. Light signals are converted to nervous system signals by cells in the retina called photoreceptors, which come in two varieties: rods and cones. Rods function in dim light but are not sensitive to color. Cones function best in bright light but are sensitive to color.

41. Pattern of Stimulation Image on retina is upside down and reversed right to left compared with the stimulus Brain corrects during processing

42. Image on the retina is upside down. Image on the retina is upside down.

43. Organization of Retina Photoreceptors at back of retina, in front of pigmented epithelium For light to reach photoreceptors, it must pass layers of neurons involved in visual processing These photoreceptors have pigments, or light-absorbing molecules, embedded in membranes within them. When light strikes a pigment, it changes shape in a way that prompts a cascade of chemical reactions that results in neurotransmitter release being inhibited between the rod or cone and its adjoining connecting cell. This lack of release sends the signal, �Photoreceptor stimulated here.� These photoreceptors have pigments, or light-absorbing molecules, embedded in membranes within them. When light strikes a pigment, it changes shape in a way that prompts a cascade of chemical reactions that results in neurotransmitter release being inhibited between the rod or cone and its adjoining connecting cell. This lack of release sends the signal, �Photoreceptor stimulated here.�

44. Organization of Retina Signals from photoreceptors are passed to bipolar sensory neurons, then to ganglion cells Axons of ganglion cells form the two optic nerves

45. The Photoreceptors Rods Contain the pigment rhodopsin Detect very dim light, changes in light intensity Cones Three kinds; detect red, blue, or green Provide color sense and daytime vision Vision signals travel from photoreceptors through two sets of adjoining cells, the latter of which have axons that come together to form the body�s optic nerves. Vision signals travel from photoreceptors through two sets of adjoining cells, the latter of which have axons that come together to form the body�s optic nerves.

46. Hearing Outer ear Middle ear Inner ear Our sense of hearing is based on the fact that vibrations result in �waves� of air molecules that are, by turns, more and less compressed than the ambient air around them. Waves of compression bump against eardrum (or tympanic membrane), which in turn vibrate. Initiates chain of vibration that ends in the fluid-filled cochlea of the inner ear. �Hair cells� in cochlea have ion channels that open and close in response to this vibration, resulting in nerve signals to the brain. Our sense of hearing is based on the fact that vibrations result in �waves� of air molecules that are, by turns, more and less compressed than the ambient air around them. Waves of compression bump against eardrum (or tympanic membrane), which in turn vibrate. Initiates chain of vibration that ends in the fluid-filled cochlea of the inner ear. �Hair cells� in cochlea have ion channels that open and close in response to this vibration, resulting in nerve signals to the brain.