Lecture 7 - Brain Anatomy PSYC 211 PDF

Introduction to Behavioral Neuroscience PSYC 211 Lecture 7 of 24 – Brain Anatomy (Chapter 2) Professor Jonathan Britt Questions? Concerns? Please write to [email protected] MIDTERM 1 – Monday, Sept. 30th...

Introduction to Behavioral Neuroscience PSYC 211 Lecture 7 of 24 – Brain Anatomy (Chapter 2) Professor Jonathan Britt Questions? Concerns? Please write to [email protected] MIDTERM 1 – Monday, Sept. 30th First letter of Midterm 1 covers lectures 1-8. Room your last name It has 56 multiple-choice questions. A The exam will start at 4:05 pm (no admittance after 4:30 pm) B It should take about an hour, but you have until 5:45 pm. C D E F G Please take the test LEA 132 H I in your assigned room  J K L M N O Sit every other seat P Q MCMED 1034 R S LEA 232 T Bring a pencil and an eraser U V W ARTS W- X 120 Y Z  Quiz 1 – Online Now Be sure to take Quiz 1 on MyCourses, which covers lectures 2-5. This quiz is worth 5% of you class grade and is a good practice for Midterm 1. You can take this quiz as many times as you want. Only your highest grade is recorded. Full credit is awarded for correctly answering at least 21 out of 25 questions in one attempt (which corresponds to a grade of 17.64 or higher in the grade book on MyCourses). The quiz will be open until the end of the semester, but you should aim to get full credit on it before next Monday, because at least ten of the midterm exam questions come directly from the Quiz 1 question bank.  THE NERVOUS SYSTEM HAS TWO PARTS Central nervous system (CNS) Everything in the brain AND spinal cord Peripheral nervous system (PNS) Any part of the nervous system outside the brain and spinal cord Sensory neurons and motor neurons typically span both regions. Parts of these cells are in the CNS and parts are in the PNS.  THE DISTINCTION BETWEEN THE CNS AND PNS IS REAL In the central nervous system, myelin is created by Oligodendrocytes. In the peripheral nervous system, myelin is created by Schwann cells. BLOOD–BRAIN BARRIER If a blue dye is injected into an animal's bloodstream, all tissue except the brain and spinal cord will be tinted blue.  EXTRACELLULAR FLUID IN THE BODY & BRAIN There are small holes in the blood vessels that course around your body. The liquid part of blood (blood plasma) continually leaks out of these holes. This liquid forms the extracellular fluid of your body (also called interstitial fluid). Extracellular fluid flows around cells providing nutrients and collecting waste. The extracellular fluid of the body is collected into lymph vessels, which carries it to lymph nodes & lymph organs. These structures make up the lymphatic system, a part of the immune system that detects and destroys invading organisms and foreign particles. Liquid in the lymphatic system (lymph) is returned to the blood supply to start the process again. Blood  Extracellular fluid  Lymph  Blood The CNS (brain and spinal cord) does not participate in the lymphatic system of the body because there are no holes in the blood vessels that pass through the brain and spinal cord. This property of the CNS is known as the blood brain barrier. Rather than letting blood plasma directly leak out of the circulatory system, the brain makes its own extracellular solution by actively picking out exactly what it needs from the blood. The liquid it makes (from scratch) is called cerebrospinal fluid (CSF).  THE NERVOUS SYSTEM HAS TWO PARTS Central nervous system (CNS) Everything in the brain and spinal cord – A projection neuron has an axon that innervates distal areas of the brain; it synapses on neurons that are far away from where the axon started. – An interneuron only synapses on local, nearby neurons. Its axon doesn’t go far. (most projection neurons release glutamate; most interneurons release GABA) Peripheral nervous system (PNS) Any part of the nervous system outside the brain and spinal cord, including – the axons of motor neurons. These axons are … Efferent fibers (outputs), bringing information away from … (the CNS). Motor neurons control muscle contraction and gland secretion. (Motor neuron cell bodies are mostly located in the CNS - in the spinal cord.) – sensory neuron dendrites and cell bodies. The axons of sensory neurons are… Afferent fibers (inputs), bringing information towards … (the CNS). Sensory neurons detect changes in the external and internal environment. (The axons of sensory neurons synapse in the CNS.) Major Divisions of the Nervous System Cranial nerves CNSPNS Spinal nerves  THE PERIPHERAL NERVOUS SYSTEM The brain and spinal cord communicate with the rest of the body via Nerves: enclosed, cable-like bundles of axons in the peripheral nervous system. Most nerves contain a mix of sensory axons and motor axons. There are two types of nerves: spinal nerves and cranial nerves. – We have 31 pairs of spinal nerves, nearly 1 pair for each vertebrae in our spine. The axons of spinal nerves enter/leave the spinal cord. – We have 12 pairs of cranial nerves, which enter/leave the brain directly. All cranial nerves (except for one) process movements and sensory information around the head and neck. The exception is the 10th cranial nerve – the vagus – which branches extensively in the upper half of the body (the thoracic and abdominal cavities). Vagus means “wandering”. The vagus nerve regulates the function of multiple organs, including the heart, lungs, digestive track, etc. You do not need to know this figure.  THE SPINAL CORD The spinal cord is a long, conical structure that is approximately as efferent thick as an adult's little finger. motor The principal function of the axons spinal cord is to bring sensory information to the brain and to bring motor fibers to effector afferent organs throughout the body sensory (glands and muscles). axons The spinal cord has a certain degree of autonomy from the brain, as various reflexive control circuits are located there.  ANATOMICAL DIRECTIONS or superior or superior Ventral or inferior or inferior Neuraxis – imaginary line that runs along the length of the CNS Anterior – in front Superior Posterior – behind or rostral Superior – above Inferior – below Anterior or Posterior or Rostral – towards the beak Caudal – towards the tail Dorsal – towards the back Ventral – towards the belly Note that the 4 terms above rotate when we refer to human spinal cord. Lateral – away from the midline Inferior Medial – toward the midline or caudal  Major Divisions of the Nervous System 12 pairs of cranial nerves CNS PNS 31 pairs of spinal nerves Somatic Autonomic - Interacts with external environment - Regulates body’s internal environment Afferent nerves carry sensory signals Afferent nerves carry sensory signals from the body’s surface TO the CNS from internal organs TO the CNS Efferent nerves carry motor signals Efferent nerves carry motor signals FROM the CNS to skeletal muscles FROM the CNS to internal organs  THE 2 COMPONENTS OF THE PERIPHERAL NERVOUS SYSTEM Somatic The somatic nervous system senses and interacts with nervous the external environment. system It controls skeletal muscles and processes sensory information relating to the outside world. Autonomic The ANS interacts with the body’s internal environment. nervous It is involved with sensing and regulating smooth muscle, system cardiac muscle, and glands. (ANS) The efferent (output) branch of the ANS has two anatomically distinct parts: the sympathetic and parasympathetic divisions.  THE 2 PARTS OF THE EFFERENT AUTONOMIC NERVOUS SYSTEM Sympathetic division Primes the body for action, particularly in life threatening situations (e.g., the fight-flight-freeze response when animals are threatened). – It is always active to some extent, as it regulates heart rate, blood flow, and the activity of nearly every organ in the body. – When strongly stimulated, it increases blood flow to organs involved in intense physical activity and shunts blood away from organs that are not necessary for immediate survival. Parasympathetic division Supports activities that occur when the body is in a relaxed state, when all is well. – It is always active to some extent, as it regulates urination, defecation, salvation, and sexual arousal. It is responsible for increasing the body's energy stores (i.e., digestion). – For simplicity, people say the parasympathetic system is involved in “feed and breed”, “rest and digest” activities.  ANATOMICAL DIVISIONS OF THE BRAIN 5 major divisions of the adult brain Medulla & Pons (in the hindbrain) Internal sensations (stretch) and internal muscles (heart, bladder) are generally processed in the medulla & pons. There are also several cranial nerve nuclei in the medulla and pons, which participate in hearing, balance, taste, and sensations and movements of the face.  Important Definitions Brain nuclei - in the brain, the word nuclei refers to a collection of neurons that are clustered together that regulate a shared function. For example, the hindbrain contains many brain nuclei. One controls breathing; another controls vomiting; etc. Contralateral - structures on the opposite side of the body (e.g., the motor cortex controls movements of the contralateral hand.) Ipsilateral - structures on the same side of body (e.g., taste is processed ipsilaterally). Taste and smell are the only sensory systems that do not have contralateral organization. Superficial – located close to the surface, close to the exterior of the animal Deep - located far away from the surface, deep in the interior of the animal Proximal – nearby Distal – far away The Hindbrain: Medulla Oblongata, Pons, Cerebellum The hindbrain is the most caudal division of the brain. It includes: 1. The most caudal part of the brain stem is the medulla oblongata, which contains a collection of brain nuclei that regulate autonomic functions, such as heart rate, blood flow, breathing, vomiting, sneezing, etc. One nucleus is area postrema, which initiates vomiting when poisons are detected. The blood–brain barrier is noticeably weak here. The medulla also contains part of the reticular formation, which regulates sleep and arousal. 2. The pons is a bulge in the brain stem that relays information between the cerebrum and cerebellum. Several cranial nerve nuclei are located here that participate in hearing, balance, taste, facial movements, and sensations of the face. Part of the reticular formation is also here. 3. The cerebellum (known as ‘little brain’) …  CEREBELLUM Cerebellar damage often results in jerky, exaggerated, poorly coordinated movements. Extensive cerebellar damage makes it impossible to stand up. The cerebellum does not initiate movement, but it contributes to the coordination, precision, and accurate timing of movements. Integrating sensory and motor information from throughout the brain and spinal cord, the cerebellum does some kind of sensorimotor integration on the timescale of milliseconds/seconds, which exerts a smoothing effect on movement and cognition. Cerebellum function is critical for picking up a cup and drinking without spilling, particularly if are also walking and ensuring your backpack isn’t sliding off and you are sore from a workout, etc. The cerebellum also plays an important role in motor learning, particularly as the body grows and changes over time (which necessitates adjustments in sensorimotor integration).  CEREBELLUM Afferent fibers to the cerebellum synapse in the superficial cerebellar cortex, a continuous thin layer of cells tightly folded in the style of an accordion. Neurons in the cerebellar cortex send axons inwards to the deep cerebellar nuclei. From there, neurons project to the brain and spinal cord. one of the deep myelinated axons cerebellar nuclei midbrain tectum cerebellar cortex medulla BRAIN ANATOMY THE MIDBRAIN: TECTUM AND TEGMENTUM The midbrain is a collection of nuclei that orchestrate complex reflexive behaviours. It consists of two major parts, the tectum and tegmentum The tectum (“roof”) appear as two pairs of bumps on the dorsal surface of the midbrain. The top 2 bumps are the superior colliculi. They are involved in orienting the animal to things in peripheral vision. The bottom 2 bumps are the inferior colliculi. They are involved in orienting to unexpected sounds. The tegmentum includes several structures that coordinate and motivate complex species-typical movements. Some areas of the tegmentum process pain and orchestrate behavioural responses to threats. THE THALAMUS AND HYPOTHALAMUS THE FOREBRAIN: HYPOTHALAMUS The hypothalamus is a bilateral structure made up of several nuclei, which generally regulate autonomic nervous system activity. The hypothalamus is involved in behaviours that directly relate to survival (i.e. the four F’s: feeding, fighting, fleeing and mating). Different hypothalamic nuclei control body temperature, sleep-wake cycles, hunger, sex, aggression, etc. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system (release of hormones into the blood stream) via the pituitary gland.  HORMONES (NON-SYNAPTIC, LONG DISTANCE CHEMICAL COMMUNICATION) Hormone Chemical substance that is released into the blood by an endocrine gland. It has effects on cells in other organs. Endocrine Gland that secretes hormones into the blood. The master regulator gland of the endocrine system is the hypothalamus, as it releases hormones that regulate the function of other endocrine glands. THE FOREBRAIN: THALAMUS The thalamus is another bilateral structure that contains several nuclei, many of which relay ascending sensory information to different regions of the cerebral cortex. For example, visual information from the eye passes through the lateral geniculate nuclei of the thalamus. Sound information from the ear passes through the medial geniculate nuclei of the thalamus. Many nuclei of the thalamus have widespread cortical projections.  THE CEREBRAL CORTEX The cerebral cortex is where sensory information enters conscious awareness. It is where our understanding of the world is formed and where we decide how to purposefully move in the world. An oversimplification The cerebral cortex is not made up of distinct nuclei (except in birds). Rather, it is a multi-layered structure Inputs (6 layers in mammals, 3 layers in reptiles). (mostly from the thalamus and other areas of cortex) Neurons are interconnected between layers in a way that gives rise to cortical Outputs (mostly to the columns, which are thought to be partially thalamus and other distinct functional units. areas of cortex)  THE FOREBRAIN: CEREBRAL CORTEX The surface of the brain is the cerebral cortex. It contains… sulci (small grooves) fissures (large or major grooves) gyri (ridges between sulci or fissures) These convolutions increase the surface area of the cerebral cortex. The outermost portion of the cerebral cortex is gray matter. There is a high concentration of cell bodies here. Beneath the gray matter is white matter, which is primarily just myelinated axons. Different Ways of Cutting the Brain Coronal cut (also known as a frontal section) Medial (toward midline) Coronal Lateral (away from midline) Sagittal cut A mid-sagittal cut means the exact middle (between the eyes) Horizontal cut Medial Lateral (toward (away from midline) midline)  The 4 Lobes of the Cerebral Cortex The cerebral cortex is classically subdivided into 4 lobes. The frontal lobe controls movement. The parietal lobe processes touch information. The occipital lobe processes visual information. The temporal lobe processes auditory information. Taste and smell are processed near the junction of the frontal, parietal, and temporal lobes inside the lateral fissure. Taste is processed in insular cortex. Smell is processed in piriform cortex.  Different views of the Cerebral Cortex The lateral fissure separates the frontal lobe and The longitudinal the temporal lobe fissure separates the two hemispheres The central sulcus separates the frontal lobe and the parietal lobe. Although two cerebral hemispheres perform somewhat different functions, perceptions and memories are unified. This unity is accomplished by the corpus callosum, a large bundle of axons that connects corresponding parts of the left and right hemispheres.  The Primary Cortical Areas Primary motor cortex (frontal lobe) contains motor neurons that synapse in the spinal cord. Different regions of primary motor cortex control different parts of the body. Somatosensory cortex (parietal lobe) is where touch information enters the cerebral cortex. Different regions of somatosensory cortex receive information from different parts of the body. Primary auditory cortex (temporal lobe) is where auditory information enters the cerebral cortex. Primary visual cortex (occipital lobe) is where visual information enters the cerebral cortex. Hidden in the lateral fissure is insular cortex where gustatory information enters the cerebral cortex.  Sensory Association Cortex Adjacent to each primary sensory area is Sensory Association Cortex, where perception takes place and memories are stored. Areas of sensory association cortex nearest to the primary sensory areas receive information from only one sensory system. Adjacent to primary motor cortex is Premotor Cortex, where movements are planned.  THE BASAL GANGLIA The basal ganglia and limbic system are often referred to as subcortical structures, since they sit beneath the cerebral cortex. The basal ganglia used to be called the primitive “reptilian” brain, but it is now clear that reptiles (and birds) have the other forebrain areas as well.  THE FOREBRAIN: BASAL GANGLIA The basal ganglia are a collection of nuclei in the forebrain (located beneath the lateral ventricles). As a circuit, they regulate intentional movements, motivation, reinforcement learning, and habits. Inputs to the basal ganglia come from all over the forebrain, especially from the frontal lobe. Some of its outputs descend to midbrain and hindbrain to regulate movement directly. Other outputs ascend to the cerebral cortex (via the thalamus) to regulate sensory processing and decision making. Many neurological disorders (the classic “movement” disorders) are associated with basal ganglia dysfunction. For example, Parkinson’s disease relates to the loss of dopamine signaling in the basal ganglia.  THE LIMBIC SYSTEM The limbic system is a collection of subcortical brain areas that regulate emotions and the formation of episodic memories. Its principal areas include the hippocampus, amygdala, and cingulate cortex. (Some areas of the cerebral cortex, thalamus, and hypothalamus that interconnect the hippocampus and amygdala are often considered to be part of the limbic system as well.)  THE FOREBRAIN: LIMBIC SYSTEM The cingulate cortex is a large area that overlies the corpus callosum. Cingulate means encircling. This region interconnects many limbic areas of the brain. The hippocampus and amygdala are hidden in the temporal lobe. The hippocampus is critical for explicit memory formation. The amygdala is critical for processing emotion, especially fear. (Don’t worry about other parts of the limbic system, such as the mammillary bodies, septum, and fornix.)