Support, Movement, Senses The Brain

Transcription

1 Support, Movement, Senses The Brain References- chapters 48, 49

2 Nervous systems consist of circuits of neurons and supporting cells By the Cambrian explosion, specialized systems of neurons enabled animals to sense and respond to their environments The simplest nervous systems (in cnidarians) have neurons arranged in nerve nets- a series of interconnected nerve cells More complex animals have nerves, in which axons of multiple neurons are bundled together

3 Figure 49.2 Nerve net Radial nerve Nerve ring Eyespot Brain Nerve cords Transverse nerve Brain Ventral nerve cord Segmental ganglia (a) Hydra (cnidarian) (b) Sea star (echinoderm) (c) Planarian (flatworm) (d) Leech (annelid) Brain Ventral nerve cord Segmental ganglia Anterior nerve ring Longitudinal nerve cords Ganglia Brain Ganglia Brain Spinal cord (dorsal nerve cord) (e) Insect (arthropod) (f) Chiton (mollusc) (g) Squid (mollusc) (h) Salamander (vertebrate) Sensory ganglia

4 Bilaterally symmetrical animals exhibit cephalization, clustering of sensory organs at the front end of body The simplest cephalized animals, flatworms, have a central nervous system (CNS)- consisting of a brain and longitudinal nerve cords The peripheral nervous system (PNS) consists of neurons carrying information into and out of the CNS

5 Figure 49.6 Central nervous system (CNS) Brain Spinal cord Cranial nerves Ganglia outside CNS Spinal nerves Peripheral nervous system (PNS)

6 Nervous system organization correlates with lifestyle Sessile molluscs (for example, clams and chitons) have simple systems, whereas more complex molluscs (for example, octopuses and squids) have more sophisticated systems

7 The Central Nervous System The spinal cord conveys information to and from the brain and generates basic patterns of locomotion Spinal cord also produces reflexes independently of the brain A reflex is the body s automatic response to a stimulus Ex: mallet triggers a knee-jerk reflex

8 Figure 49.7 Cell body of sensory neuron in dorsal root ganglion Gray matter White matter Quadriceps muscle Spinal cord (cross section) Hamstring muscle Key Sensory neuron Motor neuron Interneuron

9 The Peripheral Nervous System The PNS transmits information to and from the CNS and regulates movement and the internal environment In the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNS

10 The PNS has two efferent components: the motor system and the autonomic nervous system Motor system carries signals to skeletal muscles and is voluntary Autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary

11 The autonomic nervous system has sympathetic and parasympathetic divisions Sympathetic division regulates arousal and energy generation ( fight-or-flight response) Parasympathetic division has antagonistic effects on target organs and promotes calming and a return to rest and digest functions

12 Figure 49.9 Parasympathetic division Sympathetic division Constricts pupil of eye Dilates pupil of eye Stimulates salivary gland secretion Constricts bronchi in lungs Cervical Sympathetic ganglia Inhibits salivary gland secretion Relaxes bronchi in lungs Slows heart Accelerates heart Stimulates activity of stomach and intestines Stimulates activity of pancreas Thoracic Inhibits activity of stomach and intestines Inhibits activity of pancreas Stimulates gallbladder Lumbar Stimulates glucose release from liver; inhibits gallbladder Stimulates adrenal medulla Promotes emptying of bladder Promotes erection of genitalia Synapse Sacral Inhibits emptying of bladder Promotes ejaculation and vaginal contractions

13 The vertebrate brain is regionally specialized Brain structures are specialized for diverse functions Forebrain has activities including processing olfactory input, regulating sleep, learning Midbrain coordinates routing of sensory input Hindbrain controls involuntary activities, coordinates motor activities

14 Comparison of vertebrates shows that relative sizes of particular brain regions vary These size differences reflect the relative importance of the particular brain function Evolution has resulted in a close match between structure and function Lamprey ANCESTRAL VERTEBRATE Shark Ray-finned fish Amphibian Key Forebrain Midbrain Hindbrain Crocodilian Bird Mammal

15 Figure 49.11b Embryonic brain regions Brain structures in child and adult Forebrain Telencephalon Diencephalon Cerebrum (includes cerebral cortex, basal nuclei) Diencephalon (thalamus, hypothalamus, epithalamus) Midbrain Mesencephalon Midbrain (part of brainstem) Hindbrain Metencephalon Myelencephalon Pons (part of brainstem), cerebellum Medulla oblongata (part of brainstem) Mesencephalon Cerebrum Diencephalon Midbrain Hindbrain Metencephalon Myelencephalon Diencephalon Forebrain Telencephalon Spinal cord Midbrain Pons Medulla oblongata Cerebellum Spinal cord Brainstem Embryo at 1 month Embryo at 5 weeks Child

16 Arousal and Sleep The brainstem and cerebrum control arousal and sleep; sleep also regulated by biological clock Sleep is essential for learning and memory Some animals have evolutionary adaptations allowing substantial activity during sleep Dolphins sleep with one brain hemisphere at a time and are therefore able to swim while asleep

17 Biological Clock Regulation Cycles of sleep and wakefulness are examples of circadian rhythms, daily cycles of biological activity Such rhythms rely on a biological clock, a molecular mechanism that directs periodic gene expression and cellular activity Biological clocks are typically synchronized to light and dark cycles

18 Emotions Generation and experience of emotions involve many brain structures- the amygdala, hippocampus, thalamus- grouped as the limbic system Hypothalamus Thalamus Olfactory bulb Amygdala Hippocampus

19 The cerebral cortex controls voluntary movement and cognitive functions The cerebrum, the largest structure in the human brain, is essential for language, cognition, memory, consciousness, and awareness of our surroundings Skeletal muscle control Frontal lobe Sense of touch Integration of sensory information Parietal lobe Decision making, planning Combining images and object recognition Forming speech Temporal lobe Occipital lobe Hearing Cerebellum Processing visual stimuli, pattern recognition Language comprehension

20 Figure Max Hearing words Seeing words Min Speaking words Generating words

21 Lateralization of Function The two hemispheres make distinct contributions to brain function Left hemisphere more adept at language, math, logic Right hemisphere stronger at facial and pattern recognition, spatial relations, nonverbal thinking The two hemispheres work together by communicating through fibers of the corpus callosum

22 Many nervous system disorders can be explained in molecular terms Disorders of the nervous system include schizophrenia, depression, drug addiction, Alzheimer s disease, Parkinson s disease Genetic and environmental factors contribute to diseases of the nervous system

23 The Brain s Reward System and Drug Addiction Some drugs are addictive because they increase activity of the brain s dopamine reward ( pleasure ) system Cocaine, amphetamine, heroin, alcohol, and tobacco Drug addiction is characterized by compulsive consumption and an inability to control intake Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug

24 Alzheimer s Disease Mental deterioration characterized by confusion and memory loss- caused by formation of neurofibrillary tangles and amyloid plaques in the brain No cure for this disease- some drugs relieve symptoms Amyloid plaque Neurofibrillary tangle 20 µm

25 Parkinson s Disease A motor disorder caused by death of dopaminesecreting neurons in the midbrain Characterized by muscle tremors, flexed posture, and a shuffling gait No cure, although drugs and various other approaches may manage symptoms

26 Senses The star-nosed mole can catch insect prey in near total darkness in as little as 120 milliseconds Uses 11 pairs of appendages protruding from its nose to locate and capture prey Sensory processes convey information about an animal s environment to its brain; muscles carry out movements as instructed by the brain

27 Sensory receptors transduce stimulus energy and transmit signals to the CNS All stimuli represent forms of energy When a stimulus s input to the nervous system is processed, a motor response may be generated Mole forages along tunnel Food absent OR Food present Mole moves on Mole bites May involve a simple reflex or elaborate processing Sensory input Integration Motor output

28 Sensory pathways have four basic functions in common: Sensory reception- detection of stimuli by sensory receptors Transduction- conversion of stimulus energy; magnitude varies with stimuli intensity Transmission- to the CNS Integration- brain distinguishes stimuli from different receptors based on where they arrive in the brain

29 Types of Sensory Receptors Based on energy transduced, sensory receptors fall into five categories Mechanoreceptors Chemoreceptors Electromagnetic receptors Thermoreceptors Pain receptors

30 Hearing and Equilibrium in Mammals In most terrestrial vertebrates, sensory organs for hearing and equilibrium are closely associated in the ear For both senses, settling particles or moving fluid is detected by mechanoreceptors Ciliated receptor cells Cilia Statolith Sensory nerve fibers (axons) The statocyst is used to sense equilibrium

31 Hearing Vibrating objects create percussion waves in air, causing tympanic membrane vibration Sensory neurons The three bones of the middle ear transmit vibrations of moving air to the cochlea Vibrations create pressure waves in fluid in the cochlea that travel through the vestibular canal Tympanic membrane Cochlea

32 Hearing The ear conveys information about Volume- the amplitude of the sound wave Pitch- the frequency of the sound wave

33 Hearing and Equilibrium in Other Vertebrates Unlike mammals, fishes have only inner ears (near the brain) Fishes also have a lateral line system that contains mechanoreceptors with hair cells to detect water movement SURROUNDING WATER Lateral line Lateral line canal epidermis Water flow Opening of lateral line canal Side view Lateral line Cross section Top view Nerve Lateral nerve FISH BODY WALL Scale Segmental muscle Water flow Cupula Supporting cell Nerve fiber Action potentials Sensory hairs Hair cell

34 Diverse visual receptors of animals depend on light-absorbing pigments Animals use diverse organs for vision, but the underlying mechanism for capturing light is the same, suggesting a common evolutionary origin Light detectors range from simple clusters of cells that detect direction and intensity of light, to complex organs that form images Light detectors all contain photoreceptors, cells that contain light-absorbing pigment molecules

35 Light-Detecting Organs Most invertebrates have a light-detecting organ One of the simplest light-detecting organs is that of planarians A pair of ocelli called eyespots are located near the head These allow planarians to move away from light and seek shaded locations

36 Compound Eyes Insects and crustaceans have compound eyes, which consist of up to several thousand light detectors called ommatidia Compound eyes are effective at detecting movement Insects have excellent color vision, and some can see into the ultraviolet range

37 Single-Lens Eyes Among invertebrates, single-lens eyes are found in some jellies, polychaetes, spiders, and molluscs Work like a camera- iris changes the pupil diameter to control how much light enters Eyes of all vertebrates have a single lens- eye detects color and light, but brain assembles information and perceives an image

38 Figure 50.17a Suspensory ligament Sclera Choroid Retina Fovea Neurons Retina Photoreceptors Rod Cone Cornea Iris Pupil Optic nerve Aqueous humor Lens Vitreous humor Optic disk Central artery and vein of the retina Optic nerve fibers Ganglion cell Amacrine cell Bipolar cell Horizontal cell Pigmented epithelium

39 Color Vision Among vertebrates, most fish, amphibians, and reptiles, including birds, have good color vision In humans, perception of color is based on three types of cones (photoreceptors), each with a different visual pigment: red, green, or blue Mammals that are nocturnal usually have a high proportion of rods (photoreceptors that differentiate objects in low light) in the retina

40 Abnormal color vision results from alterations in the genes for one or more photopsin proteins In 2009, researchers studying color blindness in squirrel monkeys made a breakthrough in gene therapy

41 The senses of taste and smell rely on similar sets of sensory receptors In terrestrial animals, Gustation (taste) is dependent on the detection of chemicals called tastants; In mammals, there are five taste perceptions: sweet, sour, salty, bitter, umami Olfaction (smell) is dependent on the detection of odorant molecules In aquatic animals there is no distinction between taste and smell Taste receptors of insects are in sensory hairs located on feet and in mouth parts

42 The physical interaction of protein filaments is required for muscle function Muscle Muscle activity is a response to input from the nervous system Vertebrate skeletal muscle moves bones and the body Glycolysis and aerobic respiration generate the energy (ATP) needed to sustain muscle contraction Bundle of muscle fibers Single muscle fiber (cell) Plasma membrane Myofibril Nuclei

43 Amyotrophic lateral sclerosis (ALS), formerly called Lou Gehrig s disease, interferes with the excitation of skeletal muscle fibers; this disease is usually fatal

44 Nervous Control of Muscle Tension Contraction of a whole muscle is graded, which means that the extent and strength of its contraction can be voluntarily altered There are two basic mechanisms by which the nervous system produces graded contractions Varying the number of fibers that contract Varying the rate at which fibers are stimulated

45 Figure Spinal cord Motor unit 1 Motor unit 2 Synaptic terminals Nerve Motor neuron cell body Motor neuron axon Muscle Muscle fibers Tendon

46 Other Types of Muscle In addition to skeletal muscle, vertebrates have cardiac muscle and smooth muscle Cardiac muscle, found only in the heart, consists of striated cells electrically connected by intercalated disks Smooth muscle is found mainly in walls of hollow organs such as those of the digestive tract Contractions are relatively slow and may be initiated by the muscles themselves Contractions may also be caused by stimulation from neurons in the autonomic nervous system

47 Skeletal systems transform muscle contraction into locomotion Human forearm (internal skeleton) Grasshopper tibia (external skeleton) The skeleton provides a rigid structure to which muscles attach Flexion Biceps Extensor muscle Skeletons function in support, protection, and movement Extension Triceps Biceps Extensor muscle Flexor muscle Triceps Flexor muscle Key Contracting muscle Relaxing muscle

48 Types of Skeletal Systems The three main types of skeletons are Hydrostatic skeletons (lack hard parts) Exoskeletons (external hard parts) Endoskeletons (internal hard parts)

49 The skeletons of small and large animals have different proportions, underlying function In mammals and birds, the position of legs relative to the body is very important in determining how much weight the legs can bear

50 Types of Locomotion Most animals are capable of locomotion- active travel from place to place In locomotion, energy is expended to overcome friction and gravity

51 Locomotion on Land Walking, running, hopping, or crawling on land requires an animal to support itself and move against gravity Diverse adaptations for locomotion on land have evolved in vertebrates

52 Air poses relatively little resistance for land locomotion Maintaining balance is a prerequisite to walking, running, or hopping Crawling poses a different challenge; a crawling animal must exert more energy to overcome friction

53 Swimming In water, friction is a bigger problem than gravity Fast swimmers usually have a sleek, torpedo-like shape to minimize friction Animals swim in diverse ways Paddling with their legs as oars Jet propulsion Undulating their body and tail from side to side, or up and down

54 Flying Active flight requires that wings develop enough lift to overcome the downward force of gravity Many flying animals have adaptations that reduce body mass Ex: birds have no urinary bladder or teeth, and have relatively large bones with air-filled regions

55 Figure 50.UN01a Energy cost (cal/kg m) (log scale) Flying Running Swimming Body mass (g) (log scale)